/* ===================== CONTACT / POLICY PAGES ===================== */
.contact-wrap,
.legal-page {
  width: min(880px, 100%);
  margin: clamp(1.5rem, 4vw, 3rem) auto clamp(3rem, 7vw, 5rem);
}

.contact-card,
.legal-page {
  background: var(--white-90);
  border: 1px solid rgba(217, 200, 180, 0.9);
  border-radius: var(--radius-lg, 18px);
  box-shadow: var(--shadow-md, 0 16px 34px rgba(69, 54, 35, 0.1));
  padding: clamp(1.25rem, 4vw, 2.5rem);
}

.contact-card h1,
.legal-header h1 {
  margin: 0 0 0.55rem;
}

.contact-card > p,
.legal-intro {
  color: var(--dim, #334155);
  font-size: clamp(1rem, 1.8vw, 1.12rem);
  line-height: 1.75;
}

.contact-form {
  display: grid;
  gap: 1rem;
  margin-top: 1.35rem;
}

.form-row {
  display: grid;
  gap: 0.45rem;
}

.form-row label {
  color: var(--text, #0f172a);
  font-size: 0.95rem;
  font-weight: 700;
}

.form-row input,
.form-row textarea {
  width: 100%;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm, 10px);
  background: #fff;
  color: var(--text);
  font: inherit;
  padding: 0.85rem 0.95rem;
  outline: none;
  transition: border-color 0.2s;
}

.form-row input:focus,
.form-row textarea:focus {
  border-color: #5eead4;
  box-shadow: 0 0 0 3px rgba(20, 184, 166, 0.14);
}

.form-row textarea {
  min-height: 180px;
  resize: vertical;
}

.contact-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: fit-content;
  min-width: 170px;
  border: none;
  border-radius: 12px;
  padding: 0.9rem 1.15rem;
  background: linear-gradient(180deg, #14a590, #0b7569);
  box-shadow: 0 10px 22px var(--accent-18);
  color: #fff;
  cursor: pointer;
  font: inherit;
  font-weight: 700;
  transition: transform 0.15s ease, box-shadow 0.15s ease, opacity 0.15s ease;
}

.contact-btn:hover {
  transform: translateY(-1px);
  box-shadow: 0 14px 26px var(--accent-22);
  opacity: 0.96;
}

.contact-btn:disabled {
  cursor: not-allowed;
  opacity: 0.65;
  transform: none;
}

.form-note,
.last-updated {
  color: var(--muted, #64748b);
  font-size: 0.92rem;
}

.form-note {
  margin: -0.25rem 0 0;
}

.hp-field {
  position: absolute !important;
  left: -9999px !important;
  opacity: 0 !important;
  pointer-events: none !important;
  height: 0 !important;
  width: 0 !important;
  overflow: hidden !important;
}

.legal-header {
  padding-bottom: 1.1rem;
}

.legal-header .unit-label {
  margin-bottom: 0.65rem;
}

.last-updated {
  margin: 0;
}

.legal-intro {
  margin: 0;
}

.legal-divider {
  border: 0;
  border-top: 1px solid var(--border, #dbe4ee);
  margin: 1.6rem 0;
}

.policy-section,
.terms-section,
.legal-contact {
  border-top: 1px solid rgba(217, 200, 180, 0.72);
  padding-top: 1.25rem;
  margin-top: 1.25rem;
}

.policy-section h2,
.terms-section h2,
.legal-contact h2 {
  color: var(--text, #0f172a);
  font-size: clamp(1.22rem, 2vw, 1.55rem);
}

.policy-section h3 {
  color: var(--accent2, #0b6f63);
  font-size: 1.02rem;
  margin-top: 1.15rem;
}

.policy-section p,
.policy-section li,
.terms-section p,
.terms-section li,
.legal-contact p {
  color: var(--dim, #334155);
}

.policy-section ul,
.terms-section ul {
  padding-left: 1.25rem;
}

.policy-section li,
.terms-section li {
  margin: 0.35rem 0;
}

.policy-note {
  background: linear-gradient(135deg, var(--accent-8), rgba(183, 121, 31, 0.04));
  border: 1px solid var(--accent-18);
  border-radius: var(--radius-sm, 10px);
  margin: 1rem 0;
  padding: 1rem 1.1rem;
}

.policy-note p {
  margin: 0;
}

@media (max-width: 640px) {
  .contact-wrap,
  .legal-page {
    margin-top: 1rem;
  }

  .contact-card,
  .legal-page {
    padding: 1.1rem;
  }

  .contact-btn {
    width: 100%;
  }
}
#problemContainer {
  margin-top: 2.5rem;
}
/* ── Inline chemistry fraction (for use in table cells, cards, etc.) ── */
.chem-frac {
  display: inline-flex;
  flex-direction: column;
  align-items: center;
  text-align: center;
  vertical-align: middle;
  font-family: 'DM Mono', monospace;
  font-size: 0.9em;
  line-height: 1.15;
  margin: 0 0.2em;
}

.chem-frac .chem-frac-n {
  display: block;
  white-space: nowrap;
  padding: 0 0.18em 0.12em;
}

.chem-frac .top {
  display: block;
  white-space: nowrap;
  padding: 0 0.18em 0.12em;
  border-bottom: 1.5px solid currentColor;
}

.chem-frac .chem-frac-bar {
  display: block;
  width: 100%;
  height: 0;
  margin: 0;
  border-top: 1.5px solid var(--text, #0f172a);
  overflow: hidden;
  color: transparent;
  line-height: 0;
  font-size: 0;
}

.chem-frac .chem-frac-d,
.chem-frac .bottom {
  display: block;
  white-space: nowrap;
  padding: 0.12em 0.18em 0;
}

.chem-frac sup {
  font-size: 0.72em;
}

.nuclear-notation {
  display: inline-flex;
  align-items: center;
  gap: 0.08em;
  vertical-align: middle;
  font-family: 'DM Mono', monospace;
  font-size: 1.02em;
  line-height: 1;
}

.nuclear-notation-stack {
  display: inline-flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  font-size: 0.76em;
  line-height: 0.88;
  transform: translateY(-0.05em);
}

.nuclear-notation-symbol {
  font-size: 1.28em;
  font-weight: 600;
}

.nuclear-notation-charge {
  align-self: flex-start;
  font-size: 0.68em;
  font-weight: 700;
  line-height: 1;
  margin-left: 0.04em;
}

.tool-notation-preview {
  display: flex;
  align-items: center;
  gap: 0.85rem;
  flex-wrap: wrap;
  margin: 0.45rem 0 0.7rem;
  padding: 0.7rem 0.85rem;
  background: rgba(15, 118, 110, 0.06);
  border: 1px solid rgba(15, 118, 110, 0.14);
  border-radius: 14px;
}

.tool-notation-preview .nuclear-notation {
  font-size: 2rem;
}

.tool-notation-copy {
  min-width: 200px;
}

.tool-notation-copy strong {
  display: block;
  font-size: 1rem;
  color: var(--text);
}

.tool-notation-copy span {
  color: var(--dim);
  font-size: 0.92rem;
}
/* ============================================================
   chem.css — ChemUnlocked Global Styles
   Typography system: Lexend + readable heading scale
   ============================================================ */

:root {
  --bg: #fffaf3;
  --surface: #ffffff;
  --surface2: #fff4e6;
  --surface-soft: #fff9f0;
  --surface-alt: #f3fbf7;
  --text: #1f2933;
  --dim: #506173;
  --muted: #718096;
  --border: #eadfce;
  --border-strong: #d9c8b4;
  --accent: #0f8a7a;
  --accent2: #0b6f63;
  --green: #21865f;
  --red: #dc2626;
  --gold: #b7791f;
  --violet: #7c5cc4;

  --shadow-sm: 0 8px 24px rgba(69, 54, 35, 0.07);
  --shadow-md: 0 16px 34px rgba(69, 54, 35, 0.1);

  --radius-sm: 10px;
  --radius-md: 14px;
  --radius-lg: 18px;

  /* Color overlays and surface opacity variants */
  --white-90: var(--white-90);
  --white-88: var(--white-88);
  --white-92: var(--white-92);
  --white-82: var(--white-82);
  --white-12: rgba(255, 255, 255, 0.12);
  --dark-5: rgba(15, 23, 42, 0.05);
  --dark-6: var(--dark-6);
  --border-warm: var(--border-warm);
  --border-cool: rgba(219, 228, 238, 0.92);
  --border-slate: var(--border-slate);
  --accent-8: var(--accent-8);
  --accent-18: var(--accent-18);
  --accent-22: var(--accent-22);
  --accent-38: rgba(15, 138, 122, 0.38);
  --accent2-14: rgba(15, 118, 110, 0.14);
  --orange-14: rgba(234, 88, 12, 0.14);
  --green-14: rgba(22, 163, 74, 0.14);
  --gold-8: rgba(183, 121, 31, 0.08);

  --container: 1120px;
  --site-menu-open-height: 0px;
  --sticky-offset: 160px;
}

/* ===================== CONSOLIDATED BASE STYLES ===================== */
/* These base classes reduce duplication across 50+ components */

/* Buttons: Core primary button styles */
._btn-primary-base {
  appearance: none;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  border: 1px solid transparent;
  background: linear-gradient(180deg, #14a590, #0b7569);
  color: #fff;
  border-radius: 12px;
  padding: 0.8rem 1rem;
  font: inherit;
  font-weight: 600;
  cursor: pointer;
  transition: 0.18s ease;
  box-shadow: 0 10px 22px var(--accent-18);
  text-align: center;
  white-space: normal;
  overflow-wrap: anywhere;
}

._btn-primary-hover {
  transform: translateY(-1px);
  box-shadow: 0 14px 26px var(--accent-22);
}

/* State colors: Correct/Success */
._state-correct {
  border-color: #86efac;
  background: #ecfdf5;
  color: #166534;
}

._state-correct-shadow {
  box-shadow: 0 14px 28px rgba(22, 163, 74, 0.14);
}

/* State colors: Incorrect/Error */
._state-incorrect {
  border-color: #fdba74;
  background: #fff7ed;
  color: #9a3412;
}

._state-incorrect-shadow {
  box-shadow: 0 14px 28px rgba(234, 88, 12, 0.14);
}

/* State colors: Feedback box shared */
._feedback-base {
  min-height: 3.5rem;
  padding: 0.95rem 1rem;
  border-radius: 14px;
  border: 1px solid #cbd5e1;
  background: #f8fafc;
  color: #334155;
  box-shadow: 0 10px 26px var(--dark-6);
}

/* Grid base: Auto-fit with minmax */
._grid-auto-fit-220 {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 0.75rem;
}

._grid-auto-fit-190 {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(190px, 1fr));
  gap: 0.75rem;
}

._grid-2-cols {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.75rem;
}

._grid-3-cols {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.75rem;
}

/* Card/Panel base */
._card-base {
  background: var(--white-90);
  border: 1px solid var(--border-warm);
  border-radius: var(--radius-lg);
  padding: 1.5rem;
  box-shadow: var(--shadow-sm);
  margin: 0 0 1.25rem 0;
  min-width: 0;
}

/* Form input base */
._input-base {
  width: 100%;
  padding: 0.7rem 0.85rem;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: #fff;
  font: inherit;
  font-size: 0.93rem;
  color: var(--text);
  outline: none;
  transition: border-color 0.2s;
}

._input-base:focus {
  border-color: #5eead4;
}

/* Grid utilities: auto-fit variants for common sizes */
._grid-auto-fit-180 {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  gap: 0.75rem;
}

._grid-auto-fit-240 {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: 1rem;
}

._grid-auto-fit-280 {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 1rem;
}

._grid-4-cols {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 1rem;
}

/* ===================== RESET ===================== */
*,
*::before,
*::after {
  box-sizing: border-box;
}

html {
  font-size: 16px;
  scroll-behavior: smooth;
}

body {
  margin: 0;
  background:
    radial-gradient(circle at 8% 8%, rgba(255, 210, 122, 0.22) 0 18rem, transparent 18.2rem),
    radial-gradient(circle at 92% 4%, rgba(109, 196, 178, 0.18) 0 16rem, transparent 16.2rem),
    linear-gradient(180deg, #fffaf3 0%, #f8fbf7 46%, #eef8f5 100%);
  color: var(--text);
  font-family: 'Lexend', system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  line-height: 1.65;
  letter-spacing: 0;
  max-width: 100%;
  overflow-x: hidden;
}

body,
main,
section,
article,
header,
footer,
nav,
div {
  min-width: 0;
}

img,
svg,
video,
canvas {
  max-width: 100%;
  height: auto;
}

a {
  color: var(--accent2);
  text-decoration: none;
}

a:hover {
  text-decoration: underline;
}

p,
li,
td,
th,
.card,
.conv-result,
.solution,
.feedback,
.prob-q,
.seo-lead {
  overflow-wrap: anywhere;
  word-break: break-word;
}

/* ===================== TYPOGRAPHY ===================== */
h1,
h2,
h3,
h4 {
  margin: 0 0 0.75rem 0;
  color: var(--text);
  letter-spacing: -0.02em;
}

h1 {
  font-size: clamp(2rem, 4vw, 3rem);
  font-weight: 700;
  line-height: 1.08;
}

h2 {
  font-size: clamp(1.45rem, 2.3vw, 1.95rem);
  font-weight: 650;
  line-height: 1.16;
}

h3 {
  font-size: clamp(1.15rem, 1.8vw, 1.35rem);
  font-weight: 600;
  line-height: 1.22;
}

h4 {
  font-size: 1rem;
  font-weight: 600;
  line-height: 1.3;
}

code,
pre,
.mono,
.formula-box,
.fl-chain,
.fl-cancel,
#dimAnalysis,
.conv-result {
  font-family: 'DM Mono', ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
}

/* ===================== SHARED LAYOUT ===================== */
.site-shell,
.container {
  width: min(var(--container), calc(100% - 2rem));
  margin: 0 auto;
  max-width: 100%;
}

.container {
  padding: 0.75rem 0 2.5rem;
}

.unit-label {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  font-size: 0.77rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  color: var(--accent2);
  margin-bottom: 0.85rem;
}

.starfield {
  position: fixed;
  inset: 0;
  pointer-events: none;
  overflow: hidden;
  background-image:
    radial-gradient(circle at 14% 20%, var(--accent-8) 0 1px, transparent 1px),
    radial-gradient(circle at 68% 16%, rgba(183, 121, 31, 0.08) 0 1px, transparent 1px),
    radial-gradient(circle at 34% 78%, rgba(124, 92, 196, 0.06) 0 1px, transparent 1px),
    radial-gradient(circle at 86% 70%, rgba(15, 138, 122, 0.06) 0 1px, transparent 1px);
  opacity: 0.75;
  z-index: 0;
}

.site-header,
.site-footer,
.container {
  position: relative;
  z-index: 1;
}

/* ===================== HEADER / FOOTER ===================== */
.site-header {
  background: rgba(255, 252, 246, 0.88);
  -webkit-backdrop-filter: blur(12px);
  backdrop-filter: blur(12px);
  border-bottom: 1px solid rgba(217, 200, 180, 0.78);
  box-shadow: 0 8px 24px rgba(69, 54, 35, 0.04);
  margin-bottom: var(--site-menu-open-height, 0px);
  position: sticky;
  top: 0;
  z-index: 50;
}

.site-header-inner {
  width: min(var(--container), calc(100% - 2rem));
  margin: 0 auto;
  min-height: 72px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  max-width: 100%;
}

.site-logo {
  display: inline-flex;
  align-items: baseline;
  font-weight: 750;
  font-size: 1.45rem;
  letter-spacing: -0.03em;
  text-decoration: none;
}

.site-logo:hover {
  text-decoration: none;
}

.site-nav {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.site-nav a {
  display: inline-flex;
  align-items: center;
  color: #465869;
  font-size: 0.95rem;
  font-weight: 650;
  padding: 0.55rem 0.8rem;
  border-radius: 999px;
  transition: 0.18s ease;
}

.site-nav a:hover,
.site-nav a.active {
  background: #e8f7f2;
  color: var(--accent2);
  text-decoration: none;
}

.site-menu-toggle {
  display: none;
  align-items: center;
  justify-content: center;
  flex-direction: column;
  gap: 0.22rem;
  width: 2.9rem;
  height: 2.9rem;
  padding: 0;
  border: 1px solid var(--border-warm);
  border-radius: 999px;
  background: var(--white-92);
  color: var(--text);
  cursor: pointer;
  box-shadow: 0 8px 20px rgba(69, 54, 35, 0.08);
}

.site-menu-toggle-bar {
  display: block;
  width: 1rem;
  height: 2px;
  border-radius: 999px;
  background: currentColor;
  transition: transform 0.18s ease, opacity 0.18s ease;
}

.site-header.menu-open .site-menu-toggle-bar:nth-child(1) {
  transform: translateY(6px) rotate(45deg);
}

.site-header.menu-open .site-menu-toggle-bar:nth-child(2) {
  opacity: 0;
}

.site-header.menu-open .site-menu-toggle-bar:nth-child(3) {
  transform: translateY(-6px) rotate(-45deg);
}

.site-footer {
  margin-top: 2.5rem;
  padding: 1.25rem 0 0.25rem;
  border-top: 1px solid var(--border);
  color: var(--muted);
  font-size: 0.9rem;
}

.footer-links {
  margin-bottom: 0.35rem;
}

.footer-links a {
  color: var(--accent2);
}

.footer-links-legal {
  font-size: 0.72rem;
  color: var(--dim, #aaa);
  margin-bottom: 0.5rem;
}

.footer-links-legal a {
  color: var(--dim, #aaa);
}

@media (max-width: 980px) {
  .site-header-inner {
    position: relative;
  }

  .site-menu-toggle {
    display: inline-flex;
  }

  .site-nav {
    display: none;
    position: absolute;
    top: calc(100% + 0.35rem);
    left: 0;
    right: 0;
    flex-direction: column;
    flex-wrap: nowrap;
    gap: 0.35rem;
    padding: 0.7rem;
    border-radius: 14px;
    border: 1px solid var(--border);
    background: rgba(255, 252, 246, 0.98);
    box-shadow: 0 12px 28px rgba(69, 54, 35, 0.12);
  }

  .site-header.menu-open .site-nav {
    display: flex;
  }

  .site-nav a {
    width: 100%;
    justify-content: flex-start;
  }
}

@media (min-width: 981px) {
  .site-nav {
    display: flex;
  }
}

/* ===================== SHARED CARD / PANEL SYSTEM ===================== */
.card,
.tool-section {
  background: var(--white-82);
  border: 1px solid rgba(219, 228, 238, 0.92);
  border-radius: var(--radius-lg);
  padding: 1.5rem;
  box-shadow: var(--shadow-sm);
  margin: 0 0 1.25rem 0;
}

.card {
  background: var(--white-90);
  border: 1px solid var(--border-warm);
  min-width: 0;
}

.card-title {
  display: block;
  font-size: 1.38rem;
  font-weight: 700;
  color: var(--text);
  line-height: 1.22;
  margin-bottom: 0.7rem;
  letter-spacing: -0.015em;
}

.card-title .num {
  color: var(--muted);
  font-size: 0.8em;
  font-weight: 500;
  margin-right: 0.45rem;
}

/* Descriptive subtitle under a card title — replaces inline color:var(--accent2) pattern */
.card-intro {
  font-size: 0.9rem;
  line-height: 1.7;
  color: var(--muted);
  margin: 0.35rem 0 1rem;
}

/* Key "one sentence" lead before a bullet list */
.card-lead {
  font-size: 1.02rem;
  font-weight: 550;
  color: var(--dim);
  line-height: 1.65;
  margin: 0 0 0.75rem;
}

/* Bullet lists inside cards */
.card ul {
  margin: 0 0 0.65rem;
  padding-left: 1.35rem;
  color: var(--dim);
}

.card ul li {
  line-height: 1.72;
  margin-bottom: 0.5rem;
  overflow-wrap: anywhere;
}

.card ul li:last-child {
  margin-bottom: 0;
}

/* ── Examples-tab problem setup panel (Given / Find / Plan) ── */
.example-setup {
  margin: 0.6rem 0 0.9rem;
  padding: 0.8rem 1rem;
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  display: grid;
  gap: 0.2rem;
}

.example-setup p {
  margin: 0;
  font-size: 0.95rem;
  line-height: 1.65;
  color: var(--dim);
}

.example-setup p strong {
  color: var(--text);
}

/* ── Examples-tab intro note (replaces inline accent2 + 0.85rem pattern) ── */
.example-note {
  font-size: 0.88rem;
  color: var(--muted);
  margin: 0 0 0.85rem;
  line-height: 1.6;
}

/* ── ICE / RICE table demo block for equilibrium lessons ── */
.ice-table-example {
  margin-top: 1rem;
}

.ice-table-intro {
  margin: 0 0 0.85rem;
  color: var(--dim);
  line-height: 1.68;
}

.ice-table {
  margin-top: 0.9rem;
}

.ice-table th,
.ice-table td {
  text-align: center;
  vertical-align: middle;
}

.ice-table th:first-child,
.ice-table td:first-child {
  text-align: left;
  width: 9rem;
}

/* ── Key stat display: big number + label (reusable across units) ── */
.stat-display {
  margin: 1.25rem 0 0;
  padding: 1.1rem 1rem 1rem;
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  text-align: center;
}

.stat-display .big-number {
  font-family: 'DM Mono', ui-monospace, monospace;
  font-size: clamp(2rem, 5vw, 2.75rem);
  font-weight: 700;
  color: var(--text);
  line-height: 1;
  letter-spacing: -0.02em;
}

.stat-label {
  display: block;
  font-size: 0.85rem;
  color: var(--muted);
  margin-top: 0.35rem;
}

/* ── Context grid: 2-3 column info cards below a stat display ── */
.context-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 0.75rem;
  margin-top: 1rem;
  text-align: left;
}

.context-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 0.85rem 0.9rem;
  font-size: 0.93rem;
  color: var(--dim);
  line-height: 1.62;
}

.context-card-title {
  display: block;
  color: var(--text);
  font-weight: 600;
  font-size: 0.95rem;
  margin-bottom: 0.35rem;
}

/* Inline emphasis for key values inside context text */
.stat-value {
  color: var(--gold);
  font-weight: 600;
}

.key-fact {
  display: flex;
  gap: 0.8rem;
  align-items: flex-start;
  margin-top: 1rem;
  padding: 1rem 1.05rem;
  border-radius: var(--radius-sm);
  background: linear-gradient(135deg, var(--accent-8), rgba(183, 121, 31, 0.04));
  border: 1px solid var(--accent-18);
}

.key-fact .icon {
  color: var(--accent2);
  font-weight: 700;
  line-height: 1;
  margin-top: 0.1rem;
}

.key-fact-copy {
  flex: 1;
  min-width: 0;
}

.key-fact-copy p {
  margin: 0;
}

.key-fact-title {
  margin: 0 0 0.55rem;
  color: var(--text);
  font-weight: 700;
}

.key-fact-list {
  margin: 0;
  padding-left: 1.1rem;
  color: var(--dim);
  line-height: 1.7;
}

.key-fact-list li {
  break-inside: avoid;
  margin: 0 0 0.45rem;
}


/* ===================== INTERACTIVE TOOLS ===================== */
.tool-grid-2 {
  grid-template-columns: repeat(2, minmax(0, 1fr));
  display: grid;
  gap: 0.75rem;
  margin-top: 0.9rem;
}

.tool-grid-3 {
  grid-template-columns: repeat(3, minmax(0, 1fr));
  display: grid;
  gap: 0.75rem;
  margin-top: 0.9rem;
}

.tool-primary-action {
  margin-top: 0.9rem;
}

.tool-actions-secondary {
  margin-top: 0.9rem;
}

.tool-result-box {
  margin-top: 0.9rem;
}

.tool-grid-3[role="group"] .btn,
.tool-grid-2[role="group"] .btn {
  min-height: 4.25rem;
}

.tool-grid-3[role="group"] .btn[aria-pressed="true"],
.tool-grid-2[role="group"] .btn[aria-pressed="true"] {
  border-color: var(--accent2);
  background: #f3fbf7;
}

.tool-flow {
  display: grid;
  gap: 0.9rem;
}

.tool-flow > .tool-prompt {
  order: 1;
}

.tool-flow > .tool-panel {
  order: 2;
}

.tool-flow > .tool-context-box,
.tool-flow > .tool-context-control,
.tool-flow > .graph-wrap,
.tool-flow > .graph-wrapper,
.tool-flow > .tool-visual-panel,
.tool-flow > .formula-box:not(.tool-feedback):not(.tool-reveal):not(.tool-support),
.tool-flow > .tool-choice-row,
.tool-flow > .tool-choice-stack,
.tool-flow > .tool-mode-row {
  order: 2;
}

.tool-flow > .tool-decision {
  order: 2;
}

.tool-flow > .tool-actions,
.tool-flow > .tool-action-row,
.tool-flow > .tool-primary-action,
.tool-flow > .tool-secondary-actions {
  order: 3;
}

.tool-flow > .tool-feedback {
  order: 4;
}

.tool-flow > .tool-reveal {
  order: 5;
}

.tool-flow > .tool-support {
  order: 6;
}

.tool-prompt {
  display: grid;
  gap: 0.45rem;
}

.tool-scenario-prompt {
  padding: 1rem 1.1rem;
  margin-bottom: 1rem;
  border: 1px solid #fde68a;
  border-radius: 18px;
  background: linear-gradient(135deg, #fff8e7, #fffbeb);
  box-shadow: 0 14px 28px rgba(217, 119, 6, 0.08);
}

.tool-scenario-prompt .tool-focus-label {
  display: inline-flex;
  align-items: center;
  gap: 0.45rem;
  width: fit-content;
  padding: 0.28rem 0.65rem;
  border-radius: 999px;
  background: rgba(180, 83, 9, 0.12);
  color: #9a3412;
  font-size: 0.78rem;
  font-weight: 800;
  letter-spacing: 0.04em;
  text-transform: uppercase;
}

.tool-scenario-prompt .tool-scenario-title {
  margin: 0;
  color: var(--text);
}

.tool-scenario-prompt .tool-hint {
  margin: 0;
}

.tool-scenario-prompt .tool-scenario-text {
  margin: 0.5rem 0 0;
  padding: 0.6rem 0.9rem;
  border-left: 4px solid #14b8a6;
  border-radius: 0 10px 10px 0;
  background: rgba(20, 184, 166, 0.07);
  font-size: 1.07rem;
  font-weight: 600;
  line-height: 1.65;
  color: #0f172a;
}

.tool-scenario-prompt .tool-scenario-text strong {
  color: #0f172a;
}

.tool-prompt > :last-child {
  margin-bottom: 0;
}

.tool-hint {
  margin: 0;
  color: var(--dim);
  line-height: 1.6;
}

.tool-decision {
  display: grid;
  gap: 0.75rem;
}

.tool-primary-action,
.tool-secondary-actions,
.tool-action-row {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
}

.tool-secondary-actions {
  margin-top: 0;
}

.tool-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  margin-top: 0;
}

.tool-action-row {
  margin-top: 0;
}

.btn-primary,
.tool-primary-action .btn,
.tool-primary-action .practice-banner-btn {
  min-width: 9rem;
  min-height: 3.1rem;
}

.tool-actions .btn,
.tool-action-row .btn,
.btn-secondary,
.tool-secondary-actions .btn,
.tool-secondary-actions .practice-banner-btn {
  min-height: 2.9rem;
}

.tool-actions .btn:disabled,
.tool-action-row .btn:disabled,
.tool-secondary-actions .btn:disabled,
.tool-primary-action .btn:disabled {
  cursor: not-allowed;
  opacity: 0.58;
  transform: none;
  box-shadow: none;
}

.tool-actions .btn:disabled:hover,
.tool-action-row .btn:disabled:hover,
.tool-secondary-actions .btn:disabled:hover,
.tool-primary-action .btn:disabled:hover {
  transform: none;
  box-shadow: none;
}

.tool-feedback,
.solver-result.tool-feedback,
.en-result.tool-feedback,
.vsepr-out.tool-feedback,
.formula-box.tool-feedback {
  margin-top: 0;
  min-height: 3.5rem;
  padding: 0.95rem 1rem;
  border-radius: 14px;
  border: 1px solid #cbd5e1;
  background: #f8fafc;
  color: #334155;
  box-shadow: 0 10px 26px var(--dark-6);
}

.tool-feedback .label {
  color: #0f766e;
}

.tool-feedback[data-state="pending"],
.tool-feedback[data-state="info"] {
  border-color: #cbd5e1;
  background: #f8fafc;
  color: #334155;
}

.tool-feedback[data-state="correct"] {
  border-color: #86efac;
  background: linear-gradient(135deg, #ecfdf5, #d1fae5);
  color: #166534;
  box-shadow: 0 14px 28px rgba(22, 163, 74, 0.14);
}

.tool-feedback[data-state="incorrect"] {
  border-color: #fdba74;
  background: linear-gradient(135deg, #fff7ed, #ffedd5);
  color: #9a3412;
  box-shadow: 0 14px 28px rgba(234, 88, 12, 0.14);
}

.tool-reveal,
.tool-support {
  margin-top: 0;
}

.tool-reveal {
  padding: 1rem 1.05rem;
  border: 1px solid rgba(15, 118, 110, 0.16);
  border-radius: 16px;
  background: linear-gradient(135deg, rgba(239, 246, 255, 0.92), rgba(248, 250, 252, 0.96));
  color: var(--dim);
  box-shadow: 0 10px 26px var(--dark-6);
}

.tool-reveal-heading {
  display: block;
  margin-bottom: 0.65rem;
  color: var(--text);
}

.tool-reveal[hidden],
.tool-support[hidden] {
  display: none !important;
}

.tool-context-value {
  font-size: 1.06rem;
  font-weight: 800;
  color: var(--text);
}

.tool-context-value--lg {
  font-size: 1.15rem;
}

.content-list,
.content-ordered-list {
  color: var(--dim);
  line-height: 1.85;
  margin: 0 0 0.8rem 1.2rem;
}

.content-list:last-child,
.content-ordered-list:last-child {
  margin-bottom: 0;
}

.figure-caption,
.center-note {
  color: var(--muted);
  font-size: 0.9rem;
  line-height: 1.6;
}

.center-note {
  margin: 0.25rem auto 0;
  text-align: center;
}

.section-mini-title {
  font-size: 1.05rem;
  font-weight: 800;
  color: var(--text);
  margin: 1.6rem 0 0.5rem;
}

.figure-heading {
  font-weight: 600;
  margin: 1rem 0 0.5rem;
}

.diagram-grid-2 {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: 1rem;
  margin: 0 0 1.25rem;
}

.diagram-card {
  background: #fff;
  border: 1px solid var(--border);
  border-radius: 16px;
  padding: 1rem;
  text-align: center;
  box-shadow: var(--shadow-sm);
}

.diagram-card-title {
  font-size: 0.85rem;
  font-weight: 700;
  color: var(--text);
  margin-bottom: 0.5rem;
}

.diagram-card-note {
  margin: 0.65rem 0 0;
  font-size: 0.92rem;
  color: var(--dim);
}

.status-positive {
  color: var(--green);
}

.status-negative {
  color: var(--red);
}

.concept-panel {
  background: #fff;
  border: 1px solid var(--border);
  border-radius: 16px;
  padding: 1rem 1rem 0.5rem;
  margin: 1rem 0;
}
.concept-panel svg {
  display: block;
  width: 100%;
  max-width: 420px;
  height: auto;
  margin-inline: auto;
}

.concept-panel-title {
  font-size: 0.85rem;
  font-weight: 700;
  color: var(--text);
  margin-bottom: 0.75rem;
  text-align: center;
}

.resonance-label {
  font-size: 0.8rem;
  color: var(--dim);
}

@media (max-width: 900px) {
  .tool-grid-3 {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
}

@media (max-width: 700px) {
  .tool-grid-2,
  .tool-grid-3 {
    grid-template-columns: 1fr;
  }

  .tool-actions {
    flex-direction: column;
  }

  .tool-action-row {
    flex-direction: column;
  }

  .tool-actions .btn,
  .tool-action-row .btn,
  .tool-action-row .segment-btn {
    width: 100%;
  }

  .tool-primary-action,
  .tool-secondary-actions {
    flex-direction: column;
  }

  .tool-primary-action .btn,
  .tool-primary-action .practice-banner-btn,
  .tool-secondary-actions .btn,
  .tool-secondary-actions .practice-banner-btn {
    width: 100%;
  }
}

/* ===================== TABLES ===================== */
/* ── Scrollable table wrapper (injected by chem.js) ── */
.table-scroll-wrap {
  position: relative;
  overflow-x: auto;
  margin-top: 1rem;
  border-radius: 4px;
  transition: box-shadow 0.2s ease;
}

/* Inset shadow paints over scrollable content — stays fixed on right edge */
.table-scroll-wrap.has-overflow {
  box-shadow: inset -56px 0 30px -20px rgba(255, 255, 255, 0.96);
}

/* Caption extracted above the scroll wrapper */
.table-caption {
  font-size: 0.85rem;
  color: var(--muted);
  text-align: center;
  margin: 1rem 0 0.4rem;
  line-height: 1.4;
}

/* Hint line below the table — only shown when overflow detected */
.table-scroll-hint {
  display: none;
  font-size: 0.75rem;
  color: var(--dim, #888);
  text-align: center;
  margin: 0.3rem 0 0.6rem;
  letter-spacing: 0.04em;
  -webkit-user-select: none;
  user-select: none;
}

.table-scroll-hint.visible {
  display: block;
}

table {
  border-collapse: collapse;
  min-width: 100%;
  margin-top: 1rem;
}

.u02-separation-table {
  table-layout: fixed;
}

.u02-separation-table th:nth-child(1),
.u02-separation-table td:nth-child(1) {
  width: 26%;
}

.u02-separation-table th:nth-child(2),
.u02-separation-table td:nth-child(2) {
  width: 46%;
}

.u02-separation-table th:nth-child(3),
.u02-separation-table td:nth-child(3) {
  width: 28%;
}

.u02-separation-table th,
.u02-separation-table td {
  overflow-wrap: normal;
  word-break: normal;
  hyphens: none;
}

/* When inside the JS-injected wrapper, let the wrapper own the margin */
.table-scroll-wrap table {
  margin-top: 0;
}

thead {
  background: #f3fbf7;
  border-color: #bee5db;
  color: #174f47;
}

th,
td {
  padding: 0.8rem 0.9rem;
  border-bottom: 1px solid var(--border);
  text-align: left;
  font-size: 0.95rem;
  vertical-align: top;
  min-width: 90px;
}

th {
  color: var(--accent2);
  font-weight: 650;
  white-space: nowrap;
}

td {
  white-space: normal;
  overflow-wrap: break-word;
}

.concept-table {
  display: table;
  table-layout: fixed;
}

.concept-table th,
.concept-table td {
  white-space: normal;
  overflow-wrap: break-word;
  vertical-align: top;
}

@media (max-width: 640px) {
  .u02-separation-table th,
  .u02-separation-table td {
    padding: 0.7rem 0.7rem;
    font-size: 0.9rem;
    line-height: 1.45;
  }

  .u02-separation-table th:nth-child(1),
  .u02-separation-table td:nth-child(1) {
    width: 30%;
  }

  .u02-separation-table th:nth-child(2),
  .u02-separation-table td:nth-child(2) {
    width: 40%;
  }

  .u02-separation-table th:nth-child(3),
  .u02-separation-table td:nth-child(3) {
    width: 30%;
  }
}

/* ===================== FORMULA / STEPS ===================== */
.formula-box {
  margin-top: 1rem;
  padding: 1rem 1.1rem;
  background: #f3fbf7;
  border: 1px solid #bee5db;
  border-radius: var(--radius-sm);
  color: #174f47;
  font-family: 'Lexend', system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  font-size: clamp(1rem, 1.4vw, 1.16rem);
  font-weight: 500;
  line-height: 1.65;
  white-space: normal;
  overflow-wrap: anywhere;
  word-break: break-word;
  letter-spacing: 0.01em;
}

.formula-box .label {
  display: block;
  font-size: 0.78rem;
  color: var(--accent2);
  text-transform: uppercase;
  letter-spacing: 0.1em;
  margin-bottom: 0.45rem;
}

.formula-box strong {
  color: inherit;
}

.formula-rule-list {
  display: grid;
  gap: 0.6rem;
}

.formula-rule {
  display: block;
  font-size: 1.05em;
  line-height: 1.95;
}

.formula-rule-note {
  margin-top: 0.5rem;
  font-size: 0.92em;
  color: var(--dim);
  line-height: 2.4;
}

.particle-mole-layout {
  display: flex;
  flex-direction: column;
  gap: 0.9rem;
}

.particle-mole-defs {
  display: grid;
  gap: 0.4rem;
  font-size: 0.92em;
  line-height: 1.5;
  color: var(--dim);
}

.particle-mole-defs strong {
  color: #174f47;
}

.particle-mole-rules {
  gap: 0.45rem;
}

@media (min-width: 760px) {
  .particle-mole-layout {
    display: grid;
    grid-template-columns: minmax(0, 1.15fr) minmax(16rem, 0.85fr);
    align-items: start;
    gap: 1rem 1.2rem;
  }

  .particle-mole-rules {
    order: 1;
  }

  .particle-mole-defs {
    order: 2;
  }
}

.formula-box-list {
  padding-top: 1.05rem;
  padding-bottom: 1.05rem;
}

.formula-box-list ul {
  margin: 0;
  padding-left: 1.15rem;
  display: grid;
  gap: 0.5rem;
  font-size: 0.96em;
  line-height: 1.45;
}

.formula-box-list li {
  margin: 0;
}

.formula-frac,
.fl-frac {
  display: inline-flex;
  flex-direction: column;
  text-align: center;
  vertical-align: middle;
  align-items: center;
  min-width: max-content;
  padding: 0 0.15em;
  line-height: 1.25;
}

.formula-frac-n,
.fl-num {
  display: block;
  width: 100%;
  border-bottom: 1.5px solid currentColor;
  padding: 0 0.25em 0.15em;
  white-space: nowrap;
}

.formula-frac-d,
.fl-den {
  display: block;
  padding: 0.15em 0.25em 0;
  white-space: nowrap;
}

.particle-diagram {
  display: block;
  width: 100%;
  margin-top: 1rem;
}

#matterQuizImage {
  width: min(100%, 420px);
  margin-inline: auto;
}

.steps {
  margin-top: 1rem;
  counter-reset: step-counter;
}

.step {
  display: grid;
  grid-template-columns: auto 1fr;
  gap: 0.9rem;
  padding: 1rem 0;
  border-top: 1px solid rgba(219, 228, 238, 0.85);
}

.step:first-child {
  border-top: 0;
}

.step-num {
  counter-increment: step-counter;
  display: flex;
  align-items: center;
  justify-content: center;
  width: 28px;
  height: 28px;
  min-width: 28px;
  flex-shrink: 0;
  border-radius: 999px;
  background: linear-gradient(180deg, #14a590, #0b7569);
  color: #fff;
  font-size: 0.78rem;
  font-weight: 700;
  margin-top: 0.15rem;
}

.step-num::after {
  content: counter(step-counter);
}

/* Data-display steps (e.g. Dalton water tool) — keep as dot, no number */
.tool-context-box .step-num {
  counter-increment: none;
  width: 10px;
  height: 10px;
  min-width: 10px;
  background: #14b8a6;
  font-size: 0;
  margin-top: 0.5rem;
}

.tool-context-box .step-num::after {
  content: none;
}

.step-content p {
  margin: 0.45rem 0 0 0;
}

.sci-step-title {
  margin: 0 0 0.25rem;
  font-size: 1rem;
  font-weight: 700;
  letter-spacing: 0;
}

.practice-options {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  gap: 0.75rem;
  align-items: end;
  margin-top: 1rem;
}

.tool-label {
  display: block;
  color: var(--dim);
  font-size: 0.85rem;
  font-weight: 650;
  margin-bottom: 0.25rem;
}

.fl-label {
  font-size: 0.8rem;
  color: var(--accent2);
  letter-spacing: 0.08em;
  text-transform: uppercase;
  margin: 0.7rem 0 0.45rem;
}

.fl-chain,
.fl-cancel {
  padding: 0.85rem 0.95rem;
  border-radius: var(--radius-sm);
  background: linear-gradient(180deg, #ffffff, #fff8ed);
  border: 1px solid var(--border);
  margin: 0.55rem 0 0.65rem;
  white-space: normal;
  overflow-wrap: anywhere;
  word-break: break-word;
}

.fl-cancel {
  font-size: 0.9rem;
  color: var(--dim);
}

.fl-cancel-demo {
  line-height: 1.9;
}

.cancel-mark {
  position: relative;
  display: inline-block;
  font-weight: 700;
}

.cancel-mark::after {
  content: "";
  position: absolute;
  left: -0.06em;
  right: -0.06em;
  top: 52%;
  border-top: 3px solid currentColor;
  transform: rotate(-4deg);
  opacity: 0.95;
}

.cancel-blue {
  color: #2563eb;
}

.cancel-green {
  color: #059669;
}

.cancel-pink {
  color: #db2777;
}

.fl-result {
  color: var(--green);
  font-weight: 650;
}

.solved-display {
  display: grid;
  gap: 0.7rem;
  margin: 0.75rem 0;
}

.solved-display > .fl-chain,
.solved-display-chainline {
  margin: 0;
}

.solved-display-chainline {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.55rem;
  line-height: 1.75;
}

.solved-display-chainline .fl-frac,
.solved-display-chainline .chem-frac {
  min-width: 148px;
}

.solved-display-answerline {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.55rem;
  padding-top: 0.35rem;
  border-top: 1px dashed rgba(15, 110, 86, 0.22);
  color: var(--text);
  font-size: 1.02rem;
  line-height: 1.6;
}

.solved-display-answerline .equals-mark {
  font-weight: 700;
  color: var(--accent2);
}

.solved-display-answer .fl-result,
.solved-display-answer .chem-frac,
.solved-display-answer strong {
  color: var(--green);
  font-weight: 700;
}

.worked-solution {
  display: grid;
  gap: 0.7rem;
}

.worked-solution .solved-display {
  margin: 0;
}

.worked-solution-copy,
.worked-solution-note {
  margin: 0;
  color: var(--dim);
  line-height: 1.68;
}

.worked-solution-copy strong,
.worked-solution-note strong {
  color: var(--text);
}

.worked-solution-table {
  overflow-x: auto;
}

.worked-solution-table table {
  margin-top: 0;
}

/* ===================== TABS ===================== */
.nav-tabs {
  --tab-shell-pad: clamp(0.5rem, 1.5vw, 0.85rem);
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.55rem;
  margin: 0 calc(var(--tab-shell-pad) * -1) 1.25rem;
  position: sticky;
  top: var(--site-header-height, 72px);
  z-index: 40;
  padding: 0.65rem var(--tab-shell-pad);
  background: rgba(255, 252, 246, 0.9);
  border: 1px solid var(--border-warm);
  border-radius: 16px;
  -webkit-backdrop-filter: blur(10px);
  backdrop-filter: blur(10px);
}

.page-unit .nav-tabs {
  border-radius: 12px;
}

.tab-btn {
  appearance: none;
  border: 1.5px solid rgba(15, 138, 122, 0.28);
  background: #f4fbf9;
  color: var(--dim);
  border-radius: 999px;
  padding: 0.7rem 1rem;
  font: inherit;
  font-size: 0.9rem;
  font-weight: 550;
  cursor: pointer;
  transition: 0.18s ease;
  box-shadow: 0 2px 8px rgba(15, 138, 122, 0.08);
}

.page-unit .nav-tabs .tab-btn {
  border-radius: 14px;
}

.tab-btn:hover,
.tab-btn:focus-visible {
  border-color: rgba(15, 138, 122, 0.55);
  background: rgba(15, 138, 122, 0.07);
  color: var(--accent2);
  box-shadow: 0 4px 12px rgba(15, 138, 122, 0.12);
}

.tab-btn:active {
  background: rgba(15, 138, 122, 0.12);
  border-color: rgba(15, 138, 122, 0.65);
  box-shadow: 0 1px 3px rgba(15, 138, 122, 0.10);
  transform: scale(0.98);
}

.tab-btn.active {
  background: #e8f7f2;
  color: #0b5c51;
  border-color: #9fd5c8;
  box-shadow: inset 0 -3px 0 #0b6f63;
}

.section {
  display: none;
}

.section.active {
  display: block;
}

.concept-jump-nav {
  display: flex;
  flex-wrap: wrap;
  gap: 0.45rem;
  align-items: center;
  margin: -0.25rem 0 1.15rem;
  padding: 0.75rem 0;
}

.concept-jump-label {
  color: var(--muted);
  font-size: 0.82rem;
  font-weight: 650;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.concept-jump-nav a {
  display: inline-flex;
  align-items: center;
  min-height: 2rem;
  border: 1px solid rgba(219, 228, 238, 0.92);
  border-radius: 999px;
  padding: 0.35rem 0.8rem;
  background: var(--white-90);
  color: var(--dim);
  font-size: 0.87rem;
  font-weight: 600;
}

.concept-jump-nav a:hover {
  border-color: rgba(15, 138, 122, 0.38);
  color: var(--accent2);
  background: #f0f7ff;
  text-decoration: none;
}

.unit-bottom-nav {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.75rem;
  margin: 1.5rem 0 0;
}

.unit-bottom-link {
  min-height: 4.25rem;
  padding: 0.85rem 1rem;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  background: var(--white-82);
  box-shadow: var(--shadow-sm);
  color: var(--text);
  text-decoration: none;
}

.unit-bottom-link:hover {
  border-color: rgba(15, 138, 122, 0.38);
  color: var(--accent2);
  text-decoration: none;
}

.unit-bottom-link.is-disabled {
  opacity: 0.5;
  pointer-events: none;
}

.unit-bottom-link.is-practice {
  background: rgba(219, 234, 254, 0.55);
  border-color: #5eead4;
}

.unit-bottom-link.is-practice .unit-bottom-kicker {
  color: var(--accent2);
}

.unit-bottom-kicker {
  display: block;
  color: var(--muted);
  font-size: 0.76rem;
  font-weight: 650;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.unit-bottom-title {
  display: block;
  color: var(--accent2);
  font-size: 0.95rem;
  font-weight: 700;
  line-height: 1.25;
  margin-top: 0.2rem;
  overflow-wrap: break-word;
  word-break: break-word;
}

@media (max-width: 640px) {
  .unit-bottom-nav {
    gap: 0.5rem;
  }

  .unit-bottom-link {
    padding: 0.6rem 0.65rem;
  }

  .unit-bottom-kicker {
    font-size: 0.62rem;
  }

  .unit-bottom-title {
    font-size: 0.72rem;
  }

  th,
  td {
    padding: 0.55rem 0.65rem;
    font-size: 0.88rem;
  }
}

/* ===================== BUTTONS / INPUTS ===================== */
.btn {
  appearance: none;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  max-width: 100%;
  border: 1px solid transparent;
  background: linear-gradient(180deg, #14a590, #0b7569);
  color: #fff;
  border-radius: 12px;
  padding: 0.8rem 1rem;
  font: inherit;
  font-weight: 600;
  cursor: pointer;
  transition: 0.18s ease;
  box-shadow: 0 10px 22px var(--accent-18);
  text-align: center;
  white-space: normal;
  overflow-wrap: anywhere;
}

.btn:hover {
  transform: translateY(-1px);
  box-shadow: 0 14px 26px var(--accent-22);
}

.btn-outline {
  background: #fff;
  border-color: var(--border);
  color: var(--accent2);
  box-shadow: none;
}

.btn-outline:hover {
  border-color: #5eead4;
  background: #f0fdfa;
}

.btn-sm {
  padding: 0.55rem 0.8rem;
  font-size: 0.86rem;
  border-radius: 10px;
}

.prob-top {
  display: flex;
  align-items: center;
  gap: 0.65rem;
  margin-bottom: 0.7rem;
  flex-wrap: wrap;
}

.prob-num {
  font-weight: 700;
  color: var(--accent2);
}

.prob-tag {
  font-size: 0.76rem;
  font-weight: 650;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  padding: 0.28rem 0.5rem;
  border-radius: 999px;
}

.tag-calc {
  background: #ccfbf1;
  color: #0b6f63;
}

.tag-concept {
  background: #ecfeff;
  color: #0f766e;
}

.tag-multi {
  background: #fef3c7;
  color: #92400e;
}

.prob-q {
  font-size: 1rem;
  color: var(--text);
  margin-bottom: 0.85rem;
}

.prob-diagram-wrap {
  margin: 0 0 0.95rem;
  padding: 0.8rem;
  border-radius: 16px;
  background: linear-gradient(180deg, rgba(248, 251, 255, 0.96), rgba(239, 246, 255, 0.96));
  border: 1px solid rgba(147, 197, 253, 0.35);
}

.prob-diagram {
  display: block;
  width: min(100%, 420px);
  margin: 0 auto;
}

.prob-diagram-caption {
  margin-top: 0.55rem;
  font-size: 0.9rem;
  line-height: 1.45;
  color: var(--dim);
  text-align: center;
}

.prob-answer-area {
  margin-top: 0.4rem;
}

.prob-input {
  padding: 0.78rem 0.9rem;
  font-size: 0.98rem;
  margin-bottom: 0.5rem;
  border: 1px solid var(--border);
  border-radius: 12px;
  width: 100%;
  background: #fff;
  color: var(--text);
  outline: none;
  transition: border-color 0.2s;
}

.prob-input:focus {
  border-color: #5eead4;
}

.prob-btns {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  margin-top: 0.5rem;
}

.prob-choices {
  display: grid;
  gap: 0.55rem;
}

.choice-btn {
  appearance: none;
  width: 100%;
  max-width: 100%;
  text-align: left;
  background: #fff;
  color: var(--text);
  border: 1.5px solid #c7d7ea;
  border-radius: 12px;
  padding: 0.8rem 0.9rem;
  font: inherit;
  font-weight: 550;
  font-size: 0.97rem;
  cursor: pointer;
  transition: 0.18s ease;
}

.choice-btn:hover {
  border-color: #5eead4;
  background: #f0f7ff;
  box-shadow: inset 3px 0 0 var(--accent2);
}

.choice-btn.selected {
  border-color: #5eead4;
  background: #f0fdfa;
  box-shadow: 0 0 0 3px rgba(20, 184, 166, 0.12);
}

.choice-btn.correct,
.choice-btn.reveal-correct,
.feedback.correct {
  background: #ecfdf5;
  color: #166534;
}

.choice-btn.correct,
.choice-btn.reveal-correct {
  border-color: #86efac;
}

.choice-btn.incorrect,
.feedback.incorrect {
  background: #fef2f2;
  color: #991b1b;
}

.choice-btn.incorrect {
  border-color: #fecaca;
}

.feedback {
  display: none;
  margin-top: 0.75rem;
  padding: 0.8rem 0.95rem;
  border-radius: 12px;
  font-weight: 550;
}

.feedback:not([hidden]) {
  display: block;
}

.feedback.correct {
  border: 1px solid #bbf7d0;
}

.feedback.incorrect {
  border: 1px solid #fecaca;
}


.cu-quiz-chip {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  padding: 0.48rem 0.78rem;
  border-radius: 999px;
  background: var(--surface2);
  border: 1px solid var(--border);
  color: var(--dim);
  font-size: 0.92rem;
  font-weight: 600;
}

.cu-quiz-gallery {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(210px, 1fr));
  gap: 1rem;
  margin-top: 1rem;
}

.cu-quiz-gallery-card {
  padding: 0.95rem;
}

.cu-quiz-gallery-card h3 {
  margin: 0 0 0.5rem;
  font-size: 1rem;
}

.cu-quiz-gallery-card p {
  margin: 0.65rem 0 0;
  color: var(--dim);
}

.solution {
  display: none;
  margin-top: 0.75rem;
  padding: 0.95rem 1rem;
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: 12px;
  color: var(--dim);
}

.solution:not([hidden]) {
  display: block;
}

.solution .worked-solution-copy,
.solution .worked-solution-note {
  font-size: 0.96rem;
}

.filter-btn {
  appearance: none;
  border: 1px solid var(--border);
  background: #fff;
  color: var(--dim);
  border-radius: 999px;
  padding: 0.45rem 0.75rem;
  font: inherit;
  font-size: 0.82rem;
  cursor: pointer;
}

.filter-btn.active {
  background: #ccfbf1;
  color: var(--accent2);
  border-color: #5eead4;
}

/* ===================== UNIT PAGE — COMMON COMPONENTS ===================== */

/* Subtitle paragraph that appears under every unit <h1> */
.subtitle {
  font-size: 1.05rem;
  line-height: 1.75;
  color: var(--dim);
  max-width: 760px;
  margin: 0.5rem 0 1.5rem;
}

.section-intro {
  font-size: 0.97rem;
  line-height: 1.7;
  color: var(--dim);
  margin: 0 0 1.25rem;
}

.learning-objectives {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.65rem;
  margin: 0 0 0.95rem;
  padding: 0.7rem;
  border: 1px solid rgba(217, 200, 180, 0.52);
  border-radius: calc(var(--radius-sm) + 4px);
  background: linear-gradient(180deg, rgba(255, 255, 255, 0.44), rgba(255, 250, 242, 0.58));
  -webkit-backdrop-filter: blur(2px);
  backdrop-filter: blur(2px);
}

.learning-objectives span {
  display: flex;
  gap: 0.55rem;
  align-items: flex-start;
  min-height: 0;
  padding: 0.7rem 0.82rem;
  border: 1px solid rgba(217, 200, 180, 0.58);
  border-radius: var(--radius-sm);
  background: rgba(255, 255, 255, 0.74);
  color: var(--dim);
  font-size: 0.84rem;
  font-weight: 520;
  line-height: 1.34;
}

.learning-objectives span::before {
  content: "";
  flex: 0 0 auto;
  width: 0.48rem;
  height: 0.48rem;
  margin-top: 0.3rem;
  border-radius: 999px;
  background: var(--accent);
}

.unit-link-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(190px, 1fr));
  gap: 0.75rem;
  margin: 1.25rem 0 0;
}

.unit-link-card {
  display: block;
  padding: 1rem;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  background: var(--white-82);
  color: var(--text);
  box-shadow: var(--shadow-sm);
}

.unit-link-card:hover {
  border-color: #5eead4;
  text-decoration: none;
}

.unit-link-eyebrow {
  display: block;
  color: var(--muted);
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  margin-bottom: 0.25rem;
}

.unit-link-title {
  display: block;
  color: var(--accent2);
  font-weight: 700;
}

/* Small breadcrumb line at the bottom of every .container */
.scroll-hint {
  font-size: 0.78rem;
  color: var(--muted);
  text-align: center;
  margin-top: 2rem;
  letter-spacing: 0.04em;
}

/* ── Info callouts (Learning Objectives / Common Mistakes) ── */
/* Two-block pattern per style guide: .info-callout + .info-callout.warn  */
.info-callout {
  background: linear-gradient(135deg, rgba(15, 118, 110, 0.05), rgba(15, 118, 110, 0.02));
  border: 1px solid rgba(15, 118, 110, 0.2);
  border-left: 4px solid var(--accent2);
  border-radius: var(--radius-md);
  padding: 1.1rem 1.25rem;
  margin: 0 0 1.25rem 0;
}

.info-callout h4 {
  color: var(--accent2);
  font-size: 0.85rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  margin: 0 0 0.6rem 0;
}

.info-callout ul,
.info-callout ol {
  margin: 0;
  padding-left: 1.4rem;
}

.info-callout li {
  font-size: 0.93rem;
  color: var(--dim);
  line-height: 1.7;
  margin-bottom: 0.2rem;
}

.info-callout.warn {
  background: linear-gradient(135deg, rgba(234, 88, 12, 0.05), rgba(234, 88, 12, 0.02));
  border-color: rgba(234, 88, 12, 0.2);
  border-left-color: #ea580c;
}

.info-callout.warn h4 {
  color: #c2410c;
}

.stack-top {
  margin-top: 1rem;
}

.unit-figure {
  margin: 1rem 0 0;
}

.unit-figure img {
  display: block;
  width: min(100%, 620px);
  margin: 0 auto;
  border-radius: 14px;
  border: 1px solid var(--border);
  background: #fff;
}

.unit-figure figcaption {
  margin-top: 0.65rem;
  text-align: center;
  font-size: 0.86rem;
  color: var(--muted);
}

.unit-note {
  margin-top: 0.75rem;
  color: var(--muted);
  font-size: 0.95rem;
}

.mini-context {
  margin: 0 0 0.6rem;
  font-size: 0.9rem;
  color: var(--muted);
}

.orbital-label {
  margin-right: 0.3rem;
  font-size: 0.82rem;
}

.orbital-label-neutral {
  color: var(--muted);
}

.orbital-label-good {
  color: var(--green);
}

.orbital-label-bad {
  color: var(--red);
}

.orbital-detail {
  margin-left: 0.5rem;
  font-size: 0.83rem;
  color: var(--dim);
}

.orbital-detail-good {
  color: var(--green);
}

.orbital-detail-bad {
  color: var(--red);
}

.orb-box.forbidden {
  border-color: #fca5a5;
  background: #fef2f2;
}

.pt-color-s {
  background: #ccfbf1;
  border: 1px solid #5eead4;
}

.pt-color-p {
  background: #d1fae5;
  border: 1px solid #6ee7b7;
}

.pt-color-d {
  background: #fef3c7;
  border: 1px solid #fcd34d;
}

.pt-color-f {
  background: #fce7f3;
  border: 1px solid #f9a8d4;
}

.action-row-tight {
  margin-top: 0.65rem;
}

.action-row-spaced {
  margin-top: 1rem;
}

.quick-check-flat {
  padding-top: 0;
  border-top: none;
}

.button-top-gap {
  margin-top: 0.75rem;
}

.result-top-gap {
  margin-top: 0.75rem;
}

.config-subsection {
  margin-top: 0.8rem;
}

.config-copy {
  margin: 0.35rem 0 0;
}

.calc-note {
  display: block;
  margin-top: 0.3rem;
  font-size: 0.82rem;
  color: var(--dim);
}

/* ── Tool section wrapper + tool panel (Tools tab) ── */
.tool-section h3 {
  margin-bottom: 0.4rem;
}

.tool-desc {
  font-size: 0.93rem;
  color: var(--dim);
  margin-bottom: 0.85rem;
}

/* ── Tool panel — interactive calculator UI inside .tool-section ── */
/* Label above each input group */
.tool-panel {
  margin-top: 1rem;
  padding: 1.1rem 1.15rem;
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
}

.tool-panel label {
  display: block;
  font-size: 0.82rem;
  color: var(--accent2);
  font-weight: 600;
  margin-bottom: 0.35rem;
  text-transform: uppercase;
  letter-spacing: 0.07em;
}

/* Inputs and selects inside .tool-panel */
.tool-select,
.tool-panel input[type="text"],
.tool-panel input[type="number"],
.tool-panel select {
  width: 100%;
  padding: 0.7rem 0.85rem;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: #fff;
  font: inherit;
  font-size: 0.93rem;
  color: var(--text);
  outline: none;
  transition: border-color 0.2s;
}

.tool-select:focus,
.tool-panel input:focus,
.tool-panel select:focus {
  border-color: #5eead4;
}

/* Grid for side-by-side variable input groups */
.calc-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(190px, 1fr));
  gap: 0.85rem;
  margin-bottom: 0.75rem;
}

.calc-group {
  display: flex;
  flex-direction: column;
  gap: 0.3rem;
}

/* Monospaced result display below a tool */
.calc-result:not(.tool-feedback) {
  margin-top: 0.75rem;
  padding: 0.85rem 1rem;
  background: #fff;
  border: 1px solid var(--border);
  border-radius: 10px;
  font-family: 'DM Mono', ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  font-size: 0.9rem;
  color: var(--dim);
  line-height: 1.65;
  min-height: 2.5rem;
}

.thermochemistry-tool-grid {
  display: grid;
  grid-template-columns: minmax(260px, 0.9fr) minmax(360px, 1.1fr);
  gap: 1rem;
  align-items: start;
  margin-top: 1rem;
}

.thermochemistry-tool-grid .calc-box {
  min-width: 0;
}

.thermochemistry-tool-grid label {
  display: block;
  margin: 0.75rem 0 0.3rem;
  color: var(--dim);
  font-size: 0.82rem;
  font-weight: 650;
  letter-spacing: 0.07em;
  text-transform: uppercase;
}

.thermochemistry-tool-grid select,
.thermochemistry-tool-grid input {
  width: 100%;
  padding: 0.7rem 0.85rem;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: #fff;
  color: var(--text);
  font: inherit;
  font-size: 0.93rem;
}

/* Unit 11: Energy & Thermochemistry visuals and tools */
.tool-subtitle {
  color: var(--dim);
  line-height: 1.6;
  margin-bottom: 0.75rem;
}

.thermo-mini-title {
  font-size: 1rem;
  margin-bottom: 0.6rem;
}

.thermo-spacer {
  height: 1rem;
}

.diagram-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 1rem;
}

.diagram-card {
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  padding: 0.95rem;
}

.diagram-card img {
  width: 100%;
  height: auto;
  display: block;
  border-radius: 16px;
  background: #ffffff;
}

.diagram-card h3 {
  margin-top: 0.85rem;
  margin-bottom: 0.6rem;
}

.diagram-card-copy p:last-child {
  margin-bottom: 0;
}

.lesson-figure {
  margin: 1.1rem 0 0;
  padding: 0.95rem;
  border: 1px solid var(--border-slate);
  border-radius: 20px;
  background:
    linear-gradient(180deg, rgba(255, 255, 255, 0.96), rgba(247, 250, 252, 0.98)),
    radial-gradient(circle at top left, var(--accent-8), transparent 36%),
    radial-gradient(circle at bottom right, rgba(183, 121, 31, 0.08), transparent 34%);
  box-shadow: 0 14px 32px rgba(15, 23, 42, 0.08);
}

.lesson-figure img {
  width: 100%;
  height: auto;
  display: block;
  border-radius: 16px;
}

.lesson-figure figcaption {
  margin-top: 0.8rem;
  color: var(--dim, #334155);
  line-height: 1.65;
  font-size: 0.97rem;
}

.lesson-figure figcaption strong {
  color: var(--text, #0f172a);
}

.lesson-figure-emphasis {
  background:
    linear-gradient(180deg, rgba(255, 251, 235, 0.92), rgba(255, 255, 255, 0.98)),
    radial-gradient(circle at top right, rgba(183, 121, 31, 0.14), transparent 32%);
}

.lesson-figure-split {
  background:
    linear-gradient(180deg, rgba(240, 249, 255, 0.92), rgba(255, 255, 255, 0.98)),
    radial-gradient(circle at top left, rgba(29, 78, 216, 0.10), transparent 32%),
    radial-gradient(circle at bottom right, rgba(15, 118, 110, 0.10), transparent 30%);
}

.atomic-models-block {
  margin: 1.1rem 0 0.9rem;
  padding: 1.2rem;
  border: 1px solid var(--border-slate);
  border-radius: 24px;
  background:
    linear-gradient(180deg, rgba(255, 255, 255, 0.96), rgba(247, 250, 252, 0.98)),
    radial-gradient(circle at top left, var(--accent-8), transparent 34%),
    radial-gradient(circle at bottom right, rgba(183, 121, 31, 0.08), transparent 34%);
  box-shadow: 0 18px 38px rgba(15, 23, 42, 0.08);
}

.atomic-models-heading {
  margin-bottom: 1rem;
  padding: 1rem 1.2rem;
  border-radius: 22px;
  background: linear-gradient(90deg, #0f766e, #b7791f);
  color: #ffffff;
}

.atomic-models-heading h3 {
  margin: 0;
  color: #ffffff;
  font-size: clamp(1.4rem, 2.8vw, 2.4rem);
}

.atomic-models-heading p {
  margin: 0.35rem 0 0;
  color: var(--white-92);
  font-size: clamp(0.96rem, 1.6vw, 1.15rem);
}

.atomic-models-grid {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 1rem;
  align-items: stretch;
}

.atomic-model-card {
  display: flex;
  flex-direction: column;
  overflow: hidden;
  min-width: 0;
  border: 1px solid rgba(217, 226, 236, 0.95);
  border-radius: 22px;
  background: rgba(255, 255, 255, 0.96);
  box-shadow: 0 14px 28px rgba(15, 23, 42, 0.07);
}

.atomic-model-card img {
  display: block;
  width: 100%;
  height: auto;
  padding: 0.65rem 0.65rem 0;
}

.atomic-model-copy {
  padding: 0.35rem 1rem 1rem;
}

.atomic-model-copy h4 {
  margin: 0;
  color: var(--text, #0f172a);
  font-size: 1.2rem;
}

.atomic-model-year {
  margin: 0.2rem 0 0.7rem;
  color: #64748b;
  font-weight: 600;
}

.atomic-model-copy p {
  margin: 0.5rem 0 0;
  color: var(--dim, #334155);
  line-height: 1.55;
}

.atomic-models-summary {
  margin: 1rem 0 0;
  padding: 1rem 1.15rem;
  border: 1px solid rgba(201, 211, 225, 0.92);
  border-radius: 20px;
  background: rgba(248, 250, 252, 0.96);
  color: #334155;
  font-size: clamp(0.98rem, 1.6vw, 1.1rem);
  line-height: 1.6;
}

.atomic-models-summary strong {
  color: #0f172a;
}

.atomic-models-caption {
  margin: 0;
  color: var(--dim, #334155);
  line-height: 1.7;
  font-size: 0.98rem;
}

.gold-foil-notes {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.85rem;
  margin-top: 0.95rem;
}

.gold-foil-note {
  padding: 0.95rem 1rem;
  border-radius: 18px;
  border: 1px solid rgba(201, 211, 225, 0.92);
  background: rgba(255, 255, 255, 0.95);
}

.gold-foil-note h3 {
  margin: 0;
  font-size: 1rem;
}

.gold-foil-note p {
  margin: 0.35rem 0 0;
  color: var(--dim, #334155);
  line-height: 1.55;
}

.gold-foil-note-through {
  background: #ecfdf5;
  border-color: #7dd3a6;
}

.gold-foil-note-through h3 {
  color: #0f766e;
}

.gold-foil-note-slight {
  background: #fffbeb;
  border-color: #f3d27d;
}

.gold-foil-note-slight h3 {
  color: #b7791f;
}

.gold-foil-note-strong {
  background: #f0fdfa;
  border-color: #5eead4;
}

.gold-foil-note-strong h3 {
  color: #0b6f63;
}

@media (max-width: 1100px) {
  .atomic-models-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .gold-foil-notes {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 680px) {
  .atomic-models-block {
    padding: 0.95rem;
  }

  .atomic-models-grid {
    grid-template-columns: 1fr;
  }

  .atomic-model-copy {
    padding: 0.2rem 0.9rem 0.95rem;
  }
}

.graph-wrapper {
  width: 100%;
  overflow-x: auto;
}

.graph-wrapper svg {
  display: block;
  width: 100%;
  height: auto;
}

.legend {
  display: flex;
  flex-wrap: wrap;
  gap: 0.55rem 0.95rem;
  margin-top: 0.85rem;
}

.legend-item {
  display: inline-flex;
  align-items: center;
  gap: 0.45rem;
  color: var(--dim);
  font-size: 0.9rem;
}

.dot {
  width: 0.72rem;
  height: 0.72rem;
  border-radius: 999px;
  flex: 0 0 auto;
}

.dot.boil {
  background: #d64550;
}

.dot.steam {
  background: #8e44ad;
}

.dot.uncat {
  background: #ef4444;
}

.dot.cat {
  background: #0891b2;
}

.dot.dh-unchanged {
  background: #0f766e;
}

.segment-controls,
.profile-controls,
.tool-choice-row,
.tool-action-row,
.tool-mode-row {
  display: flex;
  flex-wrap: wrap;
  gap: 0.55rem;
  margin-top: 0.9rem;
}

.tool-action-row {
  margin-top: 1.4rem;
}

.segment-btn,
.profile-btn {
  border: 1px solid var(--border);
  background: #fff;
  color: var(--text);
  border-radius: 14px;
  padding: 0.7rem 1rem;
  font-size: 0.94rem;
  font-weight: 700;
  cursor: pointer;
  transition: all 0.18s ease;
}

.segment-btn:hover,
.profile-btn:hover {
  border-color: #5eead4;
  background: #f8fbff;
  transform: translateY(-1px);
}

.segment-btn.active,
.profile-btn.active {
  background: #0f8a7a;
  color: #fff;
  border-color: #0f8a7a;
}

.segment-btn:disabled,
.profile-btn:disabled {
  cursor: not-allowed;
  opacity: 0.42;
  transform: none !important;
  box-shadow: none !important;
  pointer-events: none;
}

.tool-choice-row[role="group"] > .tool-choice-btn,
.tool-choice-row[role="group"] > .segment-btn.tool-choice-btn,
.tool-choice-row[role="group"] > .profile-btn.tool-choice-btn,
.tool-choice-row[role="group"] > .segment-btn.explore-choice,
.tool-decision[role="group"] > .tool-choice-btn,
.tool-decision[role="group"] > .segment-btn.tool-choice-btn,
.tool-decision[role="group"] > .profile-btn.tool-choice-btn,
.tool-decision[role="group"] > .segment-btn.explore-choice {
  flex: 1 1 120px;
}

.tool-choice-btn,
.explore-choice {
  width: 100%;
  max-width: 100%;
  min-height: 2.75rem;
  border-width: 2px;
  padding: 0.7rem 1rem;
  font-size: 0.96rem;
  font-weight: 750;
  text-align: center;
  background: #fff;
  color: var(--text);
  box-shadow: 0 10px 24px var(--dark-6);
  border-radius: 18px;
}

.tool-choice-btn:hover,
.explore-choice:hover {
  border-color: #5eead4;
  background: #f0f7ff;
  box-shadow: inset 3px 0 0 var(--accent2), 0 10px 24px var(--dark-6);
}

.tool-choice-btn.active,
.explore-choice.active {
  border-color: #14b8a6;
  background: #f0fdfa;
  color: #0f766e;
  box-shadow: 0 0 0 3px rgba(20, 184, 166, 0.12);
}

.tool-choice-btn.correct,
.segment-btn.tool-choice-btn.correct,
.segment-btn.explore-choice.correct {
  border-color: #86efac;
  background: #ecfdf5;
  color: #166534;
  box-shadow: 0 12px 24px rgba(22, 163, 74, 0.14);
}

.tool-choice-btn.incorrect,
.segment-btn.tool-choice-btn.incorrect,
.segment-btn.explore-choice.incorrect {
  border-color: #fdba74;
  background: #fff7ed;
  color: #9a3412;
  box-shadow: 0 12px 24px rgba(234, 88, 12, 0.14);
}

.tool-choice-btn.cardlike,
.explore-choice.cardlike {
  border-radius: 16px;
  text-align: left;
}

.tool-choice-btn.cardlike p,
.explore-choice.cardlike p {
  margin: 0;
}

.tool-choice-btn.cardlike p + p,
.explore-choice.cardlike p + p {
  margin-top: 0.35rem;
}

.btn.tool-check-btn,
.btn.explore-check,
.tool-check-btn,
.explore-check {
  background: #b45309;
  border-color: #b45309;
  color: #fff;
  box-shadow: 0 12px 24px rgba(180, 83, 9, 0.22);
}

.btn.tool-check-btn:hover,
.btn.explore-check:hover,
.tool-check-btn:hover,
.explore-check:hover {
  background: #92400e;
  border-color: #92400e;
}

.btn.tool-reveal-btn,
.btn.explore-reveal,
.tool-reveal-btn,
.explore-reveal {
  background: #e0ecff;
  border-color: #9bbcf7;
  color: #174ea6;
  box-shadow: 0 8px 18px rgba(59, 130, 246, 0.12);
}

.btn.tool-reveal-btn:hover:not(:disabled),
.btn.explore-reveal:hover:not(:disabled),
.tool-reveal-btn:hover:not(:disabled),
.explore-reveal:hover:not(:disabled) {
  background: #0b6f63;
  border-color: #0b6f63;
  color: #fff;
  box-shadow: 0 12px 24px rgba(15, 118, 110, 0.22);
}

.btn.tool-reveal-btn:disabled,
.btn.explore-reveal:disabled,
.tool-reveal-btn:disabled,
.explore-reveal:disabled {
  background: #ebf3ff;
  border-color: #bdd2fb;
  color: #5a6f95;
  cursor: not-allowed;
}

.btn.tool-next-btn:disabled,
.btn.explore-next:disabled,
.tool-next-btn:disabled,
.explore-next:disabled {
  background: #dff8f3;
  border-color: #b5efe3;
  color: #0f766e;
  cursor: not-allowed;
}

.tool-choice-row[role="group"] {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  margin: 0;
}

.tool-choice-stack[role="group"] {
  display: grid;
  gap: 0.75rem;
  margin: 0;
}

.tool-context-grid {
  display: grid;
  gap: 0.65rem;
}

.tool-context-grid > div {
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  gap: 0.35rem;
}

.btn.tool-next-btn,
.btn.explore-next,
.tool-next-btn,
.explore-next {
  background: #0f766e;
  border-color: #0f766e;
  color: #fff;
  box-shadow: 0 12px 24px rgba(15, 118, 110, 0.22);
}

.btn.tool-next-btn:hover,
.btn.explore-next:hover,
.tool-next-btn:hover,
.explore-next:hover {
  background: #115e59;
  border-color: #115e59;
}

.tool-actions .btn {
  min-width: 9.5rem;
  min-height: 3rem;
  border-radius: 16px;
  justify-content: center;
}

.tool-check-btn:disabled,
.tool-reveal-btn:disabled,
.tool-next-btn:disabled,
.explore-check:disabled,
.explore-reveal:disabled,
.explore-next:disabled {
  box-shadow: none;
  transform: none;
}

.segment-readout:not(.tool-feedback),
.profile-readout:not(.tool-feedback) {
  margin-top: 0.8rem;
  padding: 0.85rem 0.95rem;
  border-radius: 12px;
  border: 1px solid var(--border);
  background: #fff;
  color: var(--dim);
  line-height: 1.65;
}

.segment-readout.tool-feedback,
.profile-readout.tool-feedback,
.calc-result.tool-feedback {
  min-height: 3.15rem;
}

.tool-card > .tool-feedback {
  margin-top: 0.7rem;
}

.tool-visual-panel {
  display: grid;
  gap: 0.9rem;
  margin-top: 0.15rem;
  padding: 0.95rem 1rem;
  border: 1px solid #cbd5e1;
  border-radius: 14px;
  background: #f8fbff;
}

.tool-balance-visual {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 1rem;
}

.tool-balance-column {
  flex: 1;
  text-align: center;
}

.tool-balance-particles {
  margin-top: 0.35rem;
  font-size: 1.6rem;
}

.tool-balance-particles.reactants {
  color: #0f766e;
}

.tool-balance-particles.products {
  color: #059669;
}

.tool-balance-arrow {
  flex: 1;
  text-align: center;
  color: #475569;
}

.tool-visual-svg-wrap {
  width: 100%;
  max-width: 640px;
  margin: 0 auto;
}

.tool-visual-svg-wrap svg {
  width: 100%;
  display: block;
  border-radius: 18px;
}

@media (max-width: 700px) {
  .tool-balance-visual {
    flex-direction: column;
  }
}

.profile-note {
  margin-top: 0.75rem;
  color: var(--muted);
  font-size: 0.9rem;
}

.profile-svg .base-line {
  stroke: #cbd5e1;
  stroke-width: 2;
  fill: none;
}

.curve-segment {
  opacity: 0.45;
  transition: opacity 0.2s ease, stroke-width 0.2s ease;
}

.curve-segment.active {
  opacity: 1;
  stroke-width: 6;
}

#reactionProfileSvg .cat-path,
#reactionProfileSvg .cat-ea,
#reactionProfileSvg #catPathLabel {
  opacity: 0;
  transition: opacity 0.2s ease;
}

#reactionProfileSvg.show-catalyst .cat-path,
#reactionProfileSvg.show-catalyst .cat-ea,
#reactionProfileSvg.show-catalyst #catPathLabel {
  opacity: 1;
}

#reactionProfileSvg .ea-label,
#reactionProfileSvg #uncatPathLabel,
#reactionProfileSvg #catPathLabel,
#reactionProfileSvg #dhLabel {
  paint-order: stroke;
  stroke: #ffffff;
  stroke-width: 4px;
  stroke-linejoin: round;
}

/* ── Equipment / diagram row (lab diagrams, SVG figures) ── */
/* Used when showing multiple instrument diagrams side-by-side */
.equipment-row {
  display: flex;
  flex-wrap: wrap;
  gap: 1.5rem;
  align-items: flex-start;
  margin-top: 1rem;
}

.equip-box {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.5rem;
  flex: 0 1 auto;
}

.eq-label {
  font-size: 0.82rem;
  font-weight: 650;
  color: var(--dim);
  text-align: center;
  letter-spacing: 0.03em;
}

.eq-caption {
  font-size: 0.82rem;
  color: var(--dim);
  text-align: center;
  line-height: 1.55;
  max-width: 260px;
}

.meniscus-note {
  font-size: 0.75rem;
  color: var(--muted);
  text-align: center;
  font-style: italic;
}

.method-steps {
  display: grid;
  gap: 0.75rem;
  margin-top: 0.7rem;
}

.method-step {
  display: grid;
  grid-template-columns: 42px 1fr;
  gap: 0.8rem;
  align-items: start;
  padding: 0.85rem 0.95rem;
  background: linear-gradient(180deg, #ffffff 0%, #f8fafc 100%);
  border: 1px solid rgba(148, 163, 184, 0.24);
  border-radius: 14px;
  box-shadow: 0 8px 18px rgba(15, 23, 42, 0.04);
}

.method-step-num {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 42px;
  height: 42px;
  border-radius: 999px;
  background: linear-gradient(180deg, #ccfbf1 0%, #99f6e4 100%);
  color: #0b6f63;
  font-weight: 800;
  font-size: 1rem;
  line-height: 1;
}

.method-step-content {
  min-width: 0;
}

.method-step-content strong {
  display: block;
  margin-bottom: 0.2rem;
  color: var(--text);
  font-size: 0.98rem;
  line-height: 1.35;
}

.method-step-content span {
  display: block;
  color: var(--dim);
  font-size: 0.92rem;
  line-height: 1.6;
}

/* ── Safety / hazard symbol grid (GHS symbols) ── */
.safety-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(130px, 1fr));
  gap: 0.6rem;
  margin-top: 0.85rem;
}

.safety-item {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.2rem;
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 0.75rem 0.5rem;
  text-align: center;
}

.sym {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 3.25rem;
  height: 3.25rem;
  font-size: 1.6rem;
  line-height: 1;
}

.sym svg,
.sym img {
  display: block;
  width: 100%;
  height: 100%;
  object-fit: contain;
}

.sym-name {
  font-size: 0.78rem;
  font-weight: 650;
  color: var(--text);
}

.sym-desc {
  font-size: 0.71rem;
  color: var(--muted);
  line-height: 1.4;
}
/* Inline styles extracted from 01_Learn_Intro_to_Chemistry_and_Lab_Safety.html */

.safety-ppe-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
  gap: 0.6rem;
  margin-top: 0.5rem;
}

.key-fact-row {
  flex-direction: row;
  align-items: flex-start;
}

.margin-top-09 {
  margin-top: 0.9rem;
  font-weight: 600;
}

.margin-top-1 {
  margin-top: 1rem;
  font-weight: 600;
}

.cyl-tool {
  display: grid;
  grid-template-columns: minmax(300px, 0.95fr) minmax(320px, 1.05fr);
  gap: 1rem;
  align-items: stretch;
}

.cyl-controls,
.cyl-display {
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  padding: 1rem;
}

.cyl-controls {
  display: grid;
  gap: 0.9rem;
  align-content: start;
  min-width: 0;
}

.cyl-controls .tool-action-row {
  margin-top: 0.15rem;
}

.cyl-controls-header {
  display: grid;
  gap: 0.25rem;
}

.cyl-controls-title {
  font-size: 0.8rem;
  font-weight: 750;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: #0f766e;
}

.cyl-controls-subtitle {
  color: var(--dim);
  font-size: 0.9rem;
  line-height: 1.6;
}

.cyl-field-label {
  display: block;
  color: var(--dim);
  font-size: 0.88rem;
  font-weight: 700;
}

.cyl-select {
  width: 100%;
  padding: 0.75rem 0.9rem;
  border: 1px solid var(--border);
  border-radius: 12px;
  background: #fff;
  color: var(--text);
  font: inherit;
  margin-top: 0.4rem;
  outline: none;
  transition: border-color 0.2s;
}

.cyl-select:focus {
  border-color: #5eead4;
}

.cyl-slider {
  width: 100%;
  margin-top: -0.2rem;
}

.cyl-display {
  display: grid;
  grid-template-columns: minmax(160px, 200px) minmax(220px, 1fr);
  gap: 1rem;
  align-items: center;
}

.cyl-figure-card {
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 340px;
  padding: 0.75rem;
  border-radius: 20px;
  background:
    linear-gradient(180deg, rgba(255,255,255,0.98), rgba(248,250,252,0.98)),
    radial-gradient(circle at top left, rgba(14, 165, 233, 0.08), transparent 34%);
  border: 1px solid var(--border-slate);
}

#cylSVG {
  width: 100%;
  max-width: 143px;
  height: auto;
  display: block;
}

.cyl-reading {
  display: grid;
  gap: 0.75rem;
  align-content: center;
}

.cyl-reading-label {
  font-size: 0.8rem;
  font-weight: 750;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: #0b6f63;
}

.cyl-reading-value-row {
  display: flex;
  align-items: baseline;
  gap: 0.4rem;
}

.reading-value {
  font-family: 'DM Mono', ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  font-size: 2.4rem;
  line-height: 1;
  color: var(--text);
}

.cyl-feedback-text {
  font-family: inherit;
  font-size: 1rem;
  line-height: 1.55;
  color: var(--text);
  font-weight: 600;
}

.reading-unit {
  font-family: 'DM Mono', ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  font-size: 1.1rem;
  color: var(--dim);
}

.reading-hint {
  padding: 0.8rem 0.95rem;
  border-radius: 12px;
  background: #f0fdfa;
  border: 1px solid rgba(147, 197, 253, 0.45);
  color: #064e3b;
  font-size: 0.92rem;
  line-height: 1.55;
}

.equip-box-wide {
  max-width: 320px;
  flex: 0 1 320px;
}

.flex-min-180 {
  flex: 1;
  min-width: 180px;
}

.key-fact-margin {
  margin-top: 1.25rem;
}

.cyl-tip {
  padding: 0.75rem;
  background: #fff;
  border: 1px solid var(--border);
  border-radius: 12px;
  font-size: 0.92rem;
  color: var(--dim);
  line-height: 1.6;
  max-width: 32rem;
}

.balance-display-flex {
  flex: 1;
  min-width: 200px;
  display: grid;
  gap: 0.9rem;
}

.slider-label {
  font-size: 0.9rem;
  font-weight: 600;
  display: block;
  margin-bottom: 0.3rem;
  color: var(--dim);
}

.add-sample-btn:disabled {
  opacity: 0.4;
  cursor: not-allowed;
}

.balance-tool {
  display: grid;
  grid-template-columns: minmax(280px, 1.1fr) minmax(260px, 0.9fr);
  gap: 1rem;
  align-items: start;
}

.balance-visual-card,
.balance-panel {
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  padding: 1rem;
}

.balance-visual {
  border-radius: 18px;
  padding: 0.85rem 0.95rem 1rem;
  background: linear-gradient(180deg, #f7f9fc 0%, #eef3f8 100%);
  border: 1px solid rgba(148, 163, 184, 0.28);
  box-shadow:
    inset 0 1px 0 rgba(255,255,255,0.85),
    0 10px 30px rgba(15, 23, 42, 0.05);
}

.balance-stage {
  position: relative;
  height: 72px;
  margin-bottom: -2px;
}

.balance-shadow {
  position: absolute;
  left: 50%;
  bottom: 8px;
  width: 168px;
  height: 16px;
  transform: translateX(-50%);
  border-radius: 999px;
  background: rgba(71, 85, 105, 0.22);
  filter: blur(5px);
}

.balance-pan {
  position: absolute;
  left: 50%;
  top: 21px;
  width: 228px;
  height: 28px;
  transform: translateX(-50%);
  border-radius: 999px;
  background: linear-gradient(180deg, #a7b4c8 0%, #8f9db4 100%);
  box-shadow:
    inset 0 4px 0 rgba(255,255,255,0.22),
    0 2px 0 rgba(71, 85, 105, 0.2);
}

.balance-container {
  position: absolute;
  left: 50%;
  top: 0;
  width: 92px;
  height: 54px;
  transform: translateX(-50%);
  border: 4px solid rgba(147, 197, 253, 0.95);
  border-bottom-width: 5px;
  border-radius: 8px 8px 10px 10px;
  background: linear-gradient(180deg, rgba(191, 219, 254, 0.85), rgba(147, 197, 253, 0.38));
  box-shadow:
    inset 0 0 0 1px rgba(255,255,255,0.26),
    0 4px 0 rgba(147, 197, 253, 0.35);
}

.balance-container::before {
  content: "";
  position: absolute;
  left: -8px;
  right: -8px;
  bottom: -8px;
  height: 8px;
  border-radius: 999px;
  background: rgba(147, 197, 253, 0.78);
}

.balance-sample-fill {
  position: absolute;
  left: 10px;
  right: 10px;
  bottom: 6px;
  height: 18px;
  border-radius: 8px 8px 12px 12px;
  background:
    radial-gradient(circle at 10px 8px, rgba(255,255,255,0.55) 0 1px, transparent 1.5px),
    radial-gradient(circle at 24px 15px, rgba(255,255,255,0.45) 0 1px, transparent 1.5px),
    linear-gradient(180deg, #fbbf24 0%, #d97706 100%);
  box-shadow: inset 0 2px 4px rgba(255,255,255,0.35);
  transition: height 0.18s ease;
}

.balance-console {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 164px;
  align-items: center;
  gap: 0.8rem;
  min-height: 104px;
  padding: 0.95rem 1rem 1rem;
  border-radius: 14px;
  background: linear-gradient(180deg, #53637b 0%, #47566e 100%);
  border: 1px solid #36455b;
  box-shadow:
    inset 0 2px 0 rgba(255,255,255,0.08),
    inset 0 -2px 0 rgba(15, 23, 42, 0.18);
  position: relative;
}

.balance-screen-wrap {
  min-width: 0;
}

.balance-screen {
  display: grid;
  align-content: center;
  gap: 0.55rem;
  height: 70px;
  padding: 0.75rem 0.95rem;
  border-radius: 12px;
  background: linear-gradient(180deg, #111a2f 0%, #121a2a 100%);
  border: 1px solid #263248;
  box-shadow: inset 0 0 0 1px rgba(148, 163, 184, 0.06);
}

.balance-screen-mode {
  color: #9caec7;
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.08em;
}

.balance-reading-row {
  display: flex;
  align-items: baseline;
  gap: 0.18rem;
}

.balance-reading {
  font-family: 'DM Mono', ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  font-size: 2.1rem;
  line-height: 1;
  color: #59f08b;
  letter-spacing: 0.05em;
  text-shadow: 0 0 10px rgba(89, 240, 139, 0.18);
}

.balance-unit {
  font-family: 'DM Mono', ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  font-size: 1.15rem;
  color: #73f5a0;
  font-weight: 700;
}

.balance-console-side {
  display: grid;
  grid-template-columns: 1fr auto;
  grid-template-areas:
    "tare level"
    "power level"
    "units level";
  align-items: center;
  gap: 0.5rem 0.55rem;
}

.balance-console-btn {
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 28px;
  border: 1px solid #4c5a72;
  border-radius: 6px;
  background: linear-gradient(180deg, #303d55 0%, #26334a 100%);
  color: #cad5e5;
  font: inherit;
  font-size: 0.76rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  padding: 0.45rem 0.7rem;
  cursor: pointer;
  box-shadow: inset 0 1px 0 rgba(255,255,255,0.08);
}

.balance-console-btn-primary {
  grid-area: tare;
}

.balance-console-side .balance-console-btn:nth-child(2) {
  grid-area: power;
}

.balance-console-btn-wide {
  grid-area: units;
  cursor: default;
}

.balance-level-wrap {
  grid-area: level;
  display: grid;
  justify-items: center;
  gap: 0.2rem;
  margin-left: 0.05rem;
}

.balance-level-ring {
  width: 28px;
  height: 28px;
  border-radius: 999px;
  border: 2px solid #9caec7;
  display: flex;
  align-items: center;
  justify-content: center;
  box-shadow: inset 0 0 0 1px rgba(255,255,255,0.05);
}

.balance-level-dot {
  width: 10px;
  height: 10px;
  border-radius: 999px;
  background: #59f08b;
  box-shadow: 0 0 10px rgba(89, 240, 139, 0.4);
}

.balance-level-label {
  font-size: 0.68rem;
  color: #a8b6ca;
  letter-spacing: 0.08em;
}

.balance-panel {
  display: grid;
  gap: 1rem;
}

.balance-controls {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
}

.tare-btn {
  border: 1px solid var(--border);
  border-radius: 12px;
  background: #fff;
  color: var(--text);
  font: inherit;
  font-weight: 700;
  padding: 0.75rem 1rem;
  cursor: pointer;
}

.tare-btn:disabled,
.balance-console-btn:disabled {
  opacity: 0.45;
  cursor: not-allowed;
}

.balance-mini-note {
  color: var(--dim);
  font-size: 0.88rem;
  line-height: 1.6;
}

.tare-status {
  grid-column: 1 / -1;
  margin-top: 0.9rem;
  padding: 0.85rem 1rem;
  background: #f8fafc;
  border: 1px solid var(--border);
  border-radius: 10px;
  color: var(--dim);
  font-size: 0.92rem;
}

.bal-step-msg {
  margin-top: 0.75rem;
  padding: 0.85rem 1.1rem;
  border-radius: 10px;
  border-left: 4px solid #3b82f6;
  background: #f0fdfa;
  color: #1e3a5f;
  font-size: 0.96rem;
  font-weight: 600;
  line-height: 1.55;
  transition: background 0.2s, border-color 0.2s, color 0.2s;
}
.bal-step-msg[data-state="ok"] {
  border-left-color: #16a34a;
  background: #f0fdf4;
  color: #14532d;
}
.bal-step-msg[data-state="warn"] {
  border-left-color: #d97706;
  background: #fffbeb;
  color: #78350f;
}
.bal-step-msg[data-state="error"] {
  border-left-color: #dc2626;
  background: #fef2f2;
  color: #7f1d1d;
}

.balance-log {
  grid-column: 1 / -1;
  margin-top: 1rem;
  padding: 0.85rem;
  background: #0f172a;
  border-radius: 8px;
  font-family: 'DM Mono', monospace;
  font-size: 0.82rem;
  color: #94a3b8;
  line-height: 1.7;
}

.balance-log-comment {
  color: #4ade80;
}

.tools-flex {
  display: flex;
  flex-wrap: wrap;
  gap: 1.25rem;
}

.tool-card {
  flex: 1;
  min-width: 220px;
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  padding: 1.1rem;
}

@media (max-width: 820px) {
  .cyl-tool {
    grid-template-columns: 1fr;
  }

  .cyl-display {
    grid-template-columns: 1fr;
  }

  .cyl-figure-card {
    min-height: 340px;
  }

  .balance-tool {
    grid-template-columns: 1fr;
  }

  .balance-console {
    grid-template-columns: 1fr;
  }

  .balance-console-side {
    grid-template-columns: repeat(3, minmax(0, 1fr));
    grid-template-areas:
      "tare power units"
      "level level level";
  }

  .balance-level-wrap {
    justify-self: center;
    margin-top: 0.25rem;
  }
}

@media (max-width: 540px) {
  .cyl-controls .tool-choice-row[role="group"] > .tool-choice-btn,
  .cyl-controls .tool-choice-row[role="group"] > .segment-btn.tool-choice-btn,
  .cyl-controls .tool-choice-row[role="group"] > .segment-btn.explore-choice,
  .cyl-controls .tool-action-row .segment-btn,
  .cyl-controls .tool-action-row .tool-check-btn,
  .cyl-controls .tool-action-row .tool-reveal-btn,
  .cyl-controls .tool-action-row .tool-next-btn {
    flex-basis: 100%;
  }

  .cyl-display {
    grid-template-columns: 1fr;
  }

  .cyl-figure-card {
    justify-self: center;
    width: min(100%, 148px);
  }
}

.sigfig-input,
.conv-input {
  width: 100%;
  padding: 0.65rem 0.75rem;
  border: 1px solid var(--border);
  border-radius: 8px;
  font: inherit;
  font-size: 0.95rem;
  background: #fff;
  color: var(--text);
  outline: none;
  transition: border-color 0.2s;
}

.sigfig-input:focus,
.conv-input:focus {
  border-color: #5eead4;
}

.sigfig-input {
  margin-bottom: 0.6rem;
}

.sigfig-result {
  font-family: 'DM Mono', monospace;
  font-size: 1rem;
  color: var(--accent2);
  min-height: 1.5em;
}

.sigfig-explain {
  font-size: 0.83rem;
  color: var(--dim);
  margin-top: 0.35rem;
  line-height: 1.5;
}

.conv-input {
  margin-bottom: 0.5rem;
}

.conv-selects {
  display: flex;
  gap: 0.5rem;
  margin-bottom: 0.6rem;
  flex-wrap: wrap;
}

.conv-select {
  flex: 1;
  padding: 0.5rem;
  border: 1px solid var(--border);
  border-radius: 8px;
  font: inherit;
  font-size: 0.88rem;
}

.conv-arrow {
  display: flex;
  align-items: center;
  color: var(--muted);
  font-size: 0.9rem;
}

.conv-result {
  font-family: 'DM Mono', monospace;
  font-size: 1rem;
  color: var(--accent2);
  min-height: 1.5em;
}
/* ── Card section headings (bold paragraph labels inside cards) ── */
/* Use <p class="card-section-label"> instead of inline font-weight */
.card-section-label {
  font-weight: 650;
  color: var(--text);
  margin-top: 1rem;
  margin-bottom: 0.5rem;
}

/* ===================== INDEX PAGE — HERO ===================== */
h1 .chem     { font-weight: 900; }
h1 .unlocked { font-weight: 800; letter-spacing: -0.05em; }

.hero-subtitle {
  font-size: clamp(1.02rem, 2vw, 1.2rem);
  color: var(--dim);
  line-height: 1.75;
  max-width: 62ch;
  margin: 0 0 1.2rem;
}

/* ===================== BOND COMPARISON TABLE (Unit 10) ===================== */
.bond-compare {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 0.75rem;
  margin: 1.1rem 0;
}

.bond-col {
  border-radius: var(--radius-sm);
  padding: 0.85rem 0.9rem;
  display: flex;
  flex-direction: column;
  gap: 0.55rem;
  border: 1.5px solid transparent;
}

.bond-col.ionic {
  background: rgba(220, 38, 38, 0.06);
  border-color: rgba(220, 38, 38, 0.2);
}

.bond-col.polar {
  background: rgba(15, 118, 110, 0.06);
  border-color: rgba(15, 118, 110, 0.2);
}

.bond-col.nonpolar {
  background: rgba(5, 150, 105, 0.06);
  border-color: rgba(5, 150, 105, 0.2);
}

.bc-title {
  font-weight: 700;
  font-size: 0.92rem;
  color: var(--text);
  letter-spacing: 0.01em;
}

.bond-col.ionic   .bc-title { color: #b91c1c; }
.bond-col.polar   .bc-title { color: #0b6f63; }
.bond-col.nonpolar .bc-title { color: #047857; }

.bc-stat {
  font-size: 0.82rem;
  line-height: 1.7;
  color: var(--dim);
}

.bc-example {
  font-size: 0.78rem;
  color: var(--muted);
  border-top: 1px solid rgba(0,0,0,0.07);
  padding-top: 0.45rem;
  margin-top: auto;
}

@media (max-width: 600px) {
  .bond-compare {
    grid-template-columns: 1fr;
  }
}

/* ===================== INDEX PAGE — UNITS CARD ===================== */
.units-card {
  background: linear-gradient(160deg, rgba(15, 118, 110, 0.06) 0%, rgba(255, 255, 255, 0.95) 40%);
  border: 1px solid rgba(15, 118, 110, 0.22);
  border-radius: var(--radius-lg);
  padding: 1.75rem;
  box-shadow: 0 4px 24px rgba(15, 118, 110, 0.08), var(--shadow-sm);
  margin: 0 0 1.25rem 0;
}

.units-card-header {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 1rem;
  margin-bottom: 0.65rem;
  flex-wrap: wrap;
}

.units-eyebrow {
  font-size: 0.72rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.13em;
  color: var(--accent2);
  margin-bottom: 0.45rem;
}

.units-card-title {
  font-size: 1.65rem;
  font-weight: 700;
  color: var(--text);
  line-height: 1.2;
  margin: 0;
}

.start-here-badge {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  font-size: 0.72rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  background: #ccfbf1;
  color: var(--accent2);
  border: 1px solid #99f6e4;
  padding: 0.3rem 0.7rem;
  border-radius: 999px;
  flex-shrink: 0;
  margin-top: 0.2rem;
}

.units-desc {
  font-size: 0.95rem;
  color: var(--dim);
  line-height: 1.7;
  margin: 0 0 1.25rem;
}

/* ===================== INDEX PAGE — UNIT GRID ===================== */
.unit-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(min(100%, 280px), 1fr));
  gap: 0.55rem;
  margin-bottom: 1.25rem;
}

.unit-btn {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  text-decoration: none;
  background: var(--white-90);
  border: 1px solid var(--border);
  border-left: 3px solid rgba(11, 111, 99, 0.28);
  color: var(--text);
  padding: 0.9rem 1.1rem;
  border-radius: 8px;
  font-size: 0.95rem;
  font-weight: 500;
  min-height: 4rem;
  box-shadow: 0 1px 0 rgba(15, 23, 42, 0.02);
  transition: border-color 0.18s, background 0.18s, color 0.18s, transform 0.18s, box-shadow 0.18s;
  line-height: 1.3;
}

.unit-btn:hover,
.unit-btn:focus-visible {
  border-color: var(--accent);
  border-left-color: var(--accent);
  background: #f0fdfa;
  color: var(--accent2);
  transform: translateY(-1px);
  box-shadow: 0 8px 20px rgba(15, 118, 110, 0.09);
  text-decoration: none;
  outline: none;
}

.unit-btn .unit-num {
  font-family: 'DM Mono', monospace;
  font-size: 0.72rem;
  font-weight: 700;
  color: var(--muted);
  flex-shrink: 0;
  min-width: 1.6rem;
  transition: color 0.18s;
}

.unit-btn:hover .unit-num {
  color: var(--accent);
}

/* Theme group left-border colors */
.unit-btn[data-group="structure"] { border-left-color: rgba(15, 118, 110, 0.45); }
.unit-btn[data-group="reactions"] { border-left-color: rgba(5, 150, 105, 0.45); }
.unit-btn[data-group="advanced"]  { border-left-color: rgba(15, 118, 110, 0.45); }

.unit-btn[data-group="structure"]:hover { border-left-color: var(--accent2); }
.unit-btn[data-group="reactions"]:hover { border-left-color: var(--green); }
.unit-btn[data-group="advanced"]:hover  { border-left-color: var(--accent2); }

/* ===================== INDEX PAGE — UNIT FEATURES STRIP ===================== */
.unit-features {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 0.75rem;
  margin-top: 1.25rem;
  margin-bottom: 1.5rem;
}

.unit-feature {
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 1.1rem 1rem;
  text-align: center;
  position: relative;
}

/* Colored top border per step */
.unit-feature[data-step="learn"]    { border-top: 3px solid var(--accent2); }
.unit-feature[data-step="examples"] { border-top: 3px solid #0891b2; }
.unit-feature[data-step="practice"] { border-top: 3px solid var(--green); }
.unit-feature[data-step="review"]   { border-top: 3px solid #7c3aed; }

/* Arrow connectors between steps */
.unit-feature:not(:last-child)::after {
  content: "→";
  position: absolute;
  right: -0.55rem;
  top: 50%;
  transform: translateY(-50%);
  color: var(--muted);
  font-size: 0.9rem;
  z-index: 2;
  pointer-events: none;
}

.unit-feature-icon {
  font-family: 'DM Mono', monospace;
  font-size: 0.65rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--muted);
  margin-bottom: 0.4rem;
}

.unit-feature-label {
  font-size: 1.05rem;
  font-weight: 750;
  color: var(--text);
  margin-bottom: 0.3rem;
}

.unit-feature-desc {
  font-size: 0.82rem;
  color: var(--muted);
  line-height: 1.5;
}

/* ===================== INDEX PAGE — STUDY SKILLS CARD ===================== */
.skills-card {
  background: var(--white-82);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 1.5rem 1.75rem;
  box-shadow: var(--shadow-sm);
  margin: 1.25rem 0 1.25rem 0;
}

.skills-card-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  margin-bottom: 1rem;
  flex-wrap: wrap;
}

.skills-card-title {
  font-size: 1.18rem;
  font-weight: 700;
  color: var(--text);
  margin: 0;
}

.skills-card-header .unit-label {
  margin-bottom: 0.4rem;
}

.view-all-link {
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--accent2);
  text-decoration: none;
  white-space: nowrap;
  flex-shrink: 0;
}

.view-all-link:hover { text-decoration: underline; }

/* ===================== INDEX PAGE — GUIDE CARDS ===================== */
.guides-grid {
  display: grid;
  grid-template-columns: 1fr 1fr 1fr;
  gap: 0.75rem;
  margin-top: 1rem;
  margin-bottom: 1rem;
}

.guide-card {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
  text-decoration: none;
  background: var(--white-88);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  padding: 1.1rem 1.2rem;
  transition: all 0.18s;
  color: inherit;
}

.guide-card:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
  text-decoration: none;
  color: inherit;
}

.guide-card[data-color="blue"]   { border-top: 3px solid var(--accent2); }
.guide-card[data-color="green"]  { border-top: 3px solid var(--green); }
.guide-card[data-color="purple"] { border-top: 3px solid var(--accent2); }

.guide-card-eyebrow {
  font-size: 0.68rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--muted);
}

.guide-card[data-color="blue"]   .guide-card-eyebrow { color: var(--accent2); }
.guide-card[data-color="green"]  .guide-card-eyebrow { color: var(--green); }
.guide-card[data-color="purple"] .guide-card-eyebrow { color: var(--accent2); }

.guide-card-title {
  font-size: 0.95rem;
  font-weight: 650;
  color: var(--text);
  line-height: 1.3;
  margin: 0;
}

.guide-card-desc {
  font-size: 0.82rem;
  line-height: 1.65;
  color: var(--dim);
  flex: 1;
}

.guide-card-cta {
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--accent2);
  margin-top: 0.25rem;
}

.guide-card[data-color="green"]  .guide-card-cta { color: var(--green); }
.guide-card[data-color="purple"] .guide-card-cta { color: var(--accent2); }

/* ===================== INDEX PAGE — PRACTICE BANNER ===================== */
.practice-banner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1.5rem;
  background: linear-gradient(135deg, #0b6f63 0%, #0f8a7a 56%, #b7791f 135%);
  border-radius: var(--radius-lg);
  padding: 2rem 2.5rem;
  color: #fff;
  flex-wrap: wrap;
  margin-top: 1.5rem;
}

.practice-banner-left  { flex: 1 1 300px; }

.practice-banner-eyebrow {
  font-size: 0.8rem;
  font-weight: 600;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  opacity: 0.75;
  margin-bottom: 0.4rem;
}

.practice-banner-headline {
  font-size: 1.35rem;
  font-weight: 700;
  line-height: 1.25;
  margin-bottom: 0.75rem;
}

.practice-banner-features {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
}

.practice-banner-features span {
  font-size: 0.88rem;
  opacity: 0.85;
  background: rgba(255, 255, 255, 0.12);
  padding: 0.3rem 0.65rem;
  border-radius: 6px;
}

.practice-banner-right {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.5rem;
  flex-shrink: 0;
  min-width: 0;
}

.practice-banner-btn {
  display: inline-block;
  background: #fff;
  color: var(--accent2);
  font-weight: 700;
  font-size: 1rem;
  padding: 0.85rem 1.75rem;
  border-radius: 12px;
  text-decoration: none;
  white-space: nowrap;
  transition: 0.18s ease;
  box-shadow: 0 4px 14px rgba(0, 0, 0, 0.15);
}

.practice-banner-btn:hover {
  transform: translateY(-1px);
  box-shadow: 0 8px 20px rgba(0, 0, 0, 0.2);
  text-decoration: none;
}

.practice-banner-note {
  font-size: 0.78rem;
  opacity: 0.65;
  text-align: center;
}

.practice-banner-note a {
  color: #d1fae5;
  text-decoration: underline;
  text-underline-offset: 2px;
}

.practice-banner-note a:hover {
  color: #fff;
  opacity: 1;
}

.premium-controls,
.page-end-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  align-items: center;
}

.premium-controls {
  margin-bottom: 1rem;
}

.premium-control-group {
  display: flex;
  align-items: center;
  gap: 0.45rem;
}

.premium-controls label {
  color: var(--dim);
  font-size: 0.9rem;
  font-weight: 650;
}

.premium-status {
  margin: 0;
  padding: 0.95rem 1rem;
  border-radius: 14px;
  border: 1px solid #cbd5e1;
  background: #f8fafc;
  box-shadow: 0 10px 26px var(--dark-6);
}

.premium-status--muted {
  color: var(--muted);
}

.premium-status--error {
  color: #9a3412;
  border-color: #fdba74;
  background: linear-gradient(135deg, #fff7ed, #ffedd5);
  box-shadow: 0 14px 28px rgba(234, 88, 12, 0.14);
}

.premium-controls select {
  width: min(100%, 12rem);
  padding: 0.55rem 0.75rem;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: #fff;
  color: var(--text);
  font: inherit;
}

.page-end-actions {
  justify-content: center;
  margin-top: 2rem;
}

.inline-practice-cta {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 0.75rem;
  margin: 0.5rem 0 1.5rem;
  padding: 0.9rem 1.2rem;
  background: #f3fbf7;
  border: 1px solid #bee5db;
  border-radius: 12px;
}

.inline-practice-cta-text {
  color: #174f47;
  font-size: 0.95rem;
  font-weight: 600;
}

.inline-practice-cta-link {
  color: var(--accent2);
  font-size: 0.9rem;
  font-weight: 700;
  white-space: nowrap;
}

.inline-practice-cta-link:hover {
  text-decoration: underline;
}

/* ===================== RESPONSIVE ===================== */
@media (max-width: 900px) {
  .site-header-inner {
    min-height: 0;
    padding: 0.8rem 0;
  }

  .site-nav {
    gap: 0.3rem;
  }

  .guides-grid   { grid-template-columns: 1fr 1fr; }
  .unit-features { grid-template-columns: 1fr 1fr; }
  .unit-feature:not(:last-child)::after { display: none; }
}

/* Practice page specific styles */
/* Unit 02 specific styles */
#dInput {
  display: none;
}

#densityResult {
  display: none;
  margin-top: 0.75rem;
}

/* ===== Warm tutoring visual refresh — non-duplicate rules retained below ===== */
.starfield::before,
.starfield::after {
  content: "";
  position: absolute;
  aspect-ratio: 960 / 260;
  background: url("images/nitrate_resonance.svg") center / contain no-repeat;
  pointer-events: none;
}

.starfield::before {
  top: 8rem;
  right: -4rem;
  width: min(820px, 82vw);
  opacity: 0.04;
  transform: rotate(-4deg);
}

.starfield::after {
  left: -8rem;
  bottom: 7rem;
  width: min(620px, 72vw);
  opacity: 0.03;
  transform: rotate(7deg);
}

.page-unit .starfield {
  opacity: 0.62;
}

.page-unit .starfield::before {
  top: 9rem;
  right: -6rem;
  width: min(760px, 76vw);
  opacity: 0.08;
}

.page-unit .starfield::after {
  left: -10rem;
  bottom: 8rem;
  width: min(560px, 62vw);
  opacity: 0.04;
}

.unit-label,
.units-eyebrow,
.start-eyebrow {
  color: var(--accent2);
  letter-spacing: 0.11em;
}

.subtitle,
.hero-subtitle,
.start-intro,
.units-desc,
.skills-intro {
  color: var(--dim);
}

.site-logo,
.logo-chem {
  color: var(--text);
}

.logo-unlock {
  color: var(--accent2);
  font-style: italic;
}

.problem,
.start-here,
.units-card,
.skills-card.skills-card-secondary,
.guide-card-editorial,
.unit-bottom-link {
  background: var(--white-90);
  border-color: var(--border-warm);
  box-shadow: var(--shadow-sm);
}

.start-here,
.guide-card-editorial {
  background: linear-gradient(180deg, #ffffff, #fffaf2);
}

.units-card {
  background:
    linear-gradient(145deg, rgba(255, 255, 255, 0.96), rgba(242, 251, 247, 0.96)),
    radial-gradient(circle at top right, rgba(255, 204, 128, 0.2), transparent 18rem);
}

.pt-info-panel {
  background: #f3fbf7;
  border-color: #bee5db;
  color: #174f47;
}

.key-fact .icon,
th,
.formula-box .label,
.fl-label,
.unit-bottom-title {
  color: var(--accent2);
}

.btn.btn-outline,
.start-cta .btn-outline {
  background: var(--white-92);
  border: 1px solid var(--border-strong);
  color: var(--accent2);
  box-shadow: 0 6px 16px rgba(69, 54, 35, 0.05);
}

.btn.btn-outline:hover,
.start-cta .btn-outline:hover {
  background: #f3fbf7;
  border-color: rgba(15, 138, 122, 0.32);
}

.tab-btn.tab-rich {
  display: grid;
  grid-template-columns: auto 1fr;
  grid-template-areas:
    "icon label"
    "icon hint";
  align-items: center;
  column-gap: 0.65rem;
  min-height: 48px;
  text-align: left;
}

.tab-icon {
  grid-area: icon;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 1.65rem;
  height: 1.65rem;
  border-radius: 999px;
  background: rgba(15, 138, 122, 0.22);
  color: #0a6a5e;
  font-size: 0.78rem;
  font-weight: 700;
}

.tab-label {
  grid-area: label;
  font-weight: 700;
  font-size: 0.97rem;
  line-height: 1.15;
}

.tab-hint {
  grid-area: hint;
  margin-top: 0.2rem;
  color: var(--muted);
  font-size: 0.78rem;
  font-weight: 500;
  line-height: 1.3;
}

.tab-btn:not(.active) .tab-hint {
  opacity: 0.6;
}

.tab-btn:not(.active) .tab-label {
  color: var(--dim);
  opacity: 0.75;
}

.tab-btn:not(.active):hover .tab-icon {
  background: rgba(15, 138, 122, 0.18);
  color: var(--accent2);
}

.tab-btn.active .tab-icon {
  background: rgba(11, 111, 99, 0.28);
  color: #0b6f63;
}

.tab-btn.active .tab-hint {
  color: rgba(11, 111, 99, 0.78);
}

.page-unit main > .container > header {
  max-width: 58rem;
}

.learning-objectives-intro {
  margin: 0.1rem 0 0.55rem;
  color: var(--accent2);
  font-size: 0.76rem;
  font-weight: 800;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.page-unit .nav-tabs {
  margin-top: 0.1rem;
  background: rgba(255, 252, 246, 0.96);
  box-shadow: 0 12px 28px rgba(69, 54, 35, 0.06);
}

.page-unit .tab-btn {
  background: #f4fbf9;
}

.page-unit .tab-btn.active {
  box-shadow:
    inset 0 -3px 0 #0b6f63,
    0 10px 22px rgba(15, 138, 122, 0.10);
}

.concept-jump-nav a {
  background: var(--white-90);
  border-color: var(--border-warm);
}

.start-features div,
.unit-feature {
  background: linear-gradient(180deg, #ffffff, #fff8ed);
  border-color: var(--border);
}

.scroll-hint,
.site-footer {
  color: #7a6d5c;
}

.site-footer {
  border-top-color: var(--border-warm);
}

.footer-links a {
  color: var(--accent2);
  font-weight: 650;
}

a:focus-visible,
button:focus-visible,
input:focus-visible,
select:focus-visible,
textarea:focus-visible {
  outline: 3px solid rgba(15, 138, 122, 0.24);
}

@media (max-width: 760px) {
  .learning-objectives {
    grid-template-columns: 1fr;
  }

  .tab-btn.tab-rich {
    display: flex;
    align-items: center;
    gap: 0.4rem;
    min-height: 50px;
    justify-content: center;
    padding: 0.55rem 0.35rem;
    text-align: center;
  }

  .tab-icon {
    width: 1.6rem;
    height: 1.6rem;
    font-size: 0.78rem;
    flex-shrink: 0;
  }

  .tab-label {
    font-size: 0.82rem;
  }

  .tab-hint {
    display: none;
  }

  .starfield::before {
    top: 7rem;
    right: -10rem;
    width: 680px;
    opacity: 0.08;
  }

  .starfield::after {
    display: none;
  }
}


/* ===================== HOMEPAGE ===================== */
.skip-link {
  position: absolute;
  left: -999px;
  top: auto;
  width: 1px;
  height: 1px;
  overflow: hidden;
  z-index: 1000;
  background: #fff;
  color: var(--accent2);
  padding: 0.5rem 1rem;
  border-radius: 8px;
  box-shadow: var(--shadow-md);
}

.skip-link:focus {
  left: 1rem;
  top: 1rem;
  width: auto;
  height: auto;
}

.home-hero {
  display: grid;
  grid-template-columns: minmax(0, 1.18fr) minmax(min(100%, 300px), 0.82fr);
  gap: clamp(1.25rem, 3vw, 2.5rem);
  align-items: center;
  padding: clamp(0.75rem, 2.2vw, 1.5rem) 0 clamp(1.25rem, 3vw, 2.25rem);
}

.home-hero > *,
.practice-panel > *,
.unit-card-topline > *,
.skills-card-header > *,
.unit-grid > *,
.guides-grid > *,
.unit-features > * {
  min-width: 0;
}

.home-brand {
  display: none;
  align-items: baseline;
  flex-wrap: wrap;
  max-width: 100%;
  font-size: clamp(1.8rem, 4vw, 3.5rem);
  line-height: 1;
  letter-spacing: -0.06em;
  margin-bottom: 0.85rem;
}

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

.home-brand .chem {
  font-weight: 900;
  color: #0f172a;
}

.home-brand .unlocked {
  font-weight: 600;
  font-style: italic;
  color: #0b7a6e;
  margin-left: 0.06em;
}

.home-hero h1 {
  max-width: 14.5ch;
  font-size: clamp(2.7rem, 4.7vw, 4.85rem);
  line-height: 0.98;
  letter-spacing: -0.05em;
  margin-bottom: 1.1rem;
}

.hero-actions,
.practice-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  align-items: center;
}

.practice-actions a:not(.btn) {
  display: inline-flex;
  align-items: center;
  color: var(--accent2);
  background: #fff;
  border: 1px solid var(--border);
  border-radius: 999px;
  padding: 0.4rem 0.75rem;
  font-size: 0.82rem;
  font-weight: 650;
  text-decoration: none;
}

.practice-actions a:not(.btn):hover {
  background: #f0fdfa;
}

.hero-note {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  margin-top: 1.25rem;
}

.hero-note span {
  display: inline-flex;
  align-items: center;
  border: 1px solid rgba(219, 228, 238, 0.95);
  background: rgba(255, 255, 255, 0.84);
  color: var(--dim);
  border-radius: 999px;
  padding: 0.35rem 0.7rem;
  font-size: 0.82rem;
  font-weight: 600;
}

.hero-visual {
  min-height: 330px;
  width: min(100%, 36rem);
  border: 9px solid #d1d5db;
  border-radius: var(--radius-lg);
  background:
    linear-gradient(rgba(148, 163, 184, 0.12) 1px, transparent 1px),
    linear-gradient(90deg, rgba(148, 163, 184, 0.12) 1px, transparent 1px),
    radial-gradient(circle at 18% 18%, rgba(219, 234, 254, 0.95), transparent 8rem),
    radial-gradient(circle at 85% 22%, rgba(204, 251, 241, 0.78), transparent 8rem),
    linear-gradient(135deg, #ffffff 0%, #f8fafc 58%, #eef6ff 100%);
  background-size: 28px 28px, 28px 28px, auto, auto, auto;
  box-shadow:
    inset 0 0 0 2px var(--white-90),
    inset 0 -20px 45px rgba(15, 118, 110, 0.04),
    0 20px 50px rgba(15, 23, 42, 0.1);
  position: relative;
  overflow: hidden;
  padding: 1.1rem;
  justify-self: end;
}

@media (min-width: 1361px) {
  .home-hero {
    grid-template-columns: minmax(0, 1.02fr) minmax(420px, 0.98fr);
    gap: clamp(2rem, 3vw, 3.25rem);
    align-items: start;
    padding: 0.65rem 0 1.9rem;
  }

  .home-hero h1 {
    max-width: 12.1ch;
    font-size: clamp(3.65rem, 4vw, 4.55rem);
    line-height: 0.96;
  }

  .hero-subtitle {
    max-width: 47ch;
  }

  .hero-visual {
    width: min(100%, 40rem);
    min-height: 360px;
    margin-top: 0.4rem;
  }
}

.hero-visual::before {
  content: "";
  position: absolute;
  inset: 0;
  opacity: 0.3;
  background:
    linear-gradient(110deg, transparent 0 52%, rgba(255,255,255,0.9) 53%, transparent 54%),
    linear-gradient(172deg, transparent 0 65%, rgba(15,118,110,0.12) 66%, transparent 67%);
  pointer-events: none;
}

.chalk-title,
.chalk-card,
.chalk-scribble,
.chalk-dust,
.chalk-rail {
  position: absolute;
  z-index: 1;
}

.chalk-title {
  left: 1.35rem;
  top: 1.05rem;
  color: #0f766e;
  font-family: 'DM Mono', monospace;
  font-size: 0.72rem;
  font-weight: 800;
  letter-spacing: 0.09em;
  text-transform: uppercase;
}

.chalk-card {
  color: #1e293b;
  font-family: 'DM Mono', monospace;
  font-size: clamp(0.68rem, 1.2vw, 0.82rem);
  line-height: 1.55;
  text-shadow: 0.35px 0.35px 0 rgba(15, 23, 42, 0.05);
  white-space: nowrap;
}

.chalk-card strong {
  color: #0b6f63;
  font-weight: 800;
}

.chalk-card em {
  color: #0f766e;
  font-style: normal;
  font-weight: 800;
}

.chalk-card sup,
.chalk-card sub,
.chalk-reaction sub {
  font-size: 0.7em;
  line-height: 0;
}

.chalk-card.large {
  font-size: clamp(0.9rem, 1.8vw, 1.12rem);
}

.chalk-card.medium {
  font-size: clamp(0.76rem, 1.42vw, 0.93rem);
}

.chalk-card.small {
  font-size: clamp(0.62rem, 1vw, 0.76rem);
}

.chalk-card.one {
  left: 1.35rem;
  top: 3.15rem;
  transform: rotate(-1.5deg);
}

.chalk-card.two {
  right: 1.25rem;
  top: 2.95rem;
  transform: rotate(1.2deg);
  color: #0b6f63;
}

.chalk-card.three {
  left: 1.75rem;
  bottom: 4.2rem;
  transform: rotate(1deg);
  color: #334155;
}

.chalk-card.four {
  right: 1.35rem;
  bottom: 4.65rem;
  transform: rotate(-1deg);
  color: #0f766e;
}

.chalk-card.five {
  left: 38%;
  top: 42%;
  transform: translate(-50%, -50%) rotate(-0.5deg);
  color: #7c2d12;
}

.chalk-scribble {
  border: 2px solid rgba(15, 118, 110, 0.25);
  border-radius: 50%;
  transform: rotate(-11deg);
}

.chalk-scribble.one {
  width: 8.5rem;
  height: 3.2rem;
  left: 30%;
  top: 13%;
}

.chalk-scribble.two {
  width: 11rem;
  height: 4.4rem;
  right: 8%;
  bottom: 27%;
  transform: rotate(9deg);
  border-color: rgba(15, 118, 110, 0.28);
}

.chalk-dust {
  width: 0.22rem;
  height: 0.22rem;
  border-radius: 50%;
  background: rgba(15, 118, 110, 0.18);
  box-shadow:
    4.2rem 1.1rem 0 rgba(15, 118, 110, 0.16),
    7.8rem 4.5rem 0 rgba(15, 118, 110, 0.14),
    13.5rem 2.2rem 0 rgba(124, 45, 18, 0.14),
    18rem 7rem 0 rgba(15, 118, 110, 0.14),
    22rem 3.7rem 0 rgba(15, 118, 110, 0.14);
}

.chalk-rail {
  left: 1rem;
  right: 1rem;
  bottom: 1rem;
  height: 0.5rem;
  border-radius: 999px;
  background: linear-gradient(90deg, #cbd5e1, #e2e8f0);
  box-shadow: 0 -1px 0 rgba(148, 163, 184, 0.5);
}

.chalk-piece {
  position: absolute;
  right: 1.35rem;
  bottom: 0.62rem;
  width: 3.4rem;
  height: 0.45rem;
  border-radius: 999px;
  background: linear-gradient(90deg, #0f766e 0 32%, #f8fafc 32% 42%, #0f766e 42% 72%, #f8fafc 72% 82%, #dc2626 82%);
}

.chalk-eraser {
  position: absolute;
  left: 1.5rem;
  bottom: 0.58rem;
  width: 3.6rem;
  height: 0.8rem;
  border-radius: 6px;
  background: linear-gradient(180deg, #94a3b8, #64748b);
}

.chalk-reaction {
  position: absolute;
  left: 50%;
  bottom: 1.85rem;
  transform: translateX(-50%);
  font-family: 'DM Mono', monospace;
  color: #0b6f63;
  font-size: clamp(0.82rem, 1.6vw, 1rem);
  font-weight: 800;
  white-space: nowrap;
}

/* ===================== INDEX PAGE — APPROACH STRIP ===================== */
.approach-strip {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 0.85rem;
  margin: 0 0 1.25rem;
}

.approach-item {
  background: var(--white-88);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  padding: 1.25rem 1.15rem;
  display: flex;
  flex-direction: column;
  gap: 0.45rem;
}

.approach-mark {
  display: inline-flex;
  width: fit-content;
  font-size: 0.7rem;
  font-weight: 800;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  padding: 0.25rem 0.65rem;
  border-radius: 999px;
  margin-bottom: 0.1rem;
}

.approach-mark.blue,
.approach-mark.green,
.approach-mark.purple { background: #ccfbf1; color: #065f46; }

.approach-label {
  font-size: 0.96rem;
  font-weight: 700;
  color: var(--text);
  line-height: 1.3;
  margin: 0;
}

.approach-desc {
  font-size: 0.84rem;
  color: var(--dim);
  line-height: 1.65;
  margin: 0;
}

@media (max-width: 700px) {
  .approach-strip {
    grid-template-columns: 1fr;
    gap: 0.45rem;
  }
  .approach-item {
    flex-direction: row;
    align-items: center;
    gap: 0.85rem;
    padding: 0.7rem 1rem;
  }
  .approach-mark {
    white-space: nowrap;
    flex-shrink: 0;
  }
  .approach-label {
    flex: 1;
    min-width: 0;
  }
  .approach-desc { display: none; }

  /* how-it-works.html: restore full cards on mobile */
  .approach-strip--full {
    grid-template-columns: 1fr;
  }
  .approach-strip--full .approach-item {
    flex-direction: column;
    align-items: flex-start;
    padding: 1.25rem 1.15rem;
  }
  .approach-strip--full .approach-desc { display: block; }
}

.practice-panel {
  display: grid;
  grid-template-columns: minmax(0, 1.2fr) minmax(min(100%, 250px), 0.8fr);
  gap: 1.25rem;
  align-items: center;
  background: linear-gradient(135deg, #065f54 0%, #0b7a6e 55%, #0f8a7a 100%);
  color: #fff;
  border-radius: var(--radius-lg);
  padding: clamp(1.4rem, 4vw, 2.25rem);
  margin: 0 0 1.25rem;
  box-shadow: 0 16px 44px rgba(11, 111, 99, 0.2);
}

.practice-panel h2,
.practice-panel p {
  color: #fff;
}

.practice-panel .unit-label {
  color: #d1fae5;
  margin-bottom: 0.45rem;
}

.practice-panel h2 {
  margin-bottom: 0.5rem;
}

.practice-panel p {
  max-width: 68ch;
  margin: 0 0 1rem;
  opacity: 0.92;
}

.practice-panel p a {
  color: #d1fae5;
  text-decoration: underline;
  text-underline-offset: 2px;
}

.practice-panel p a:hover {
  color: #fff;
}

.practice-panel .btn {
  background: #fff;
  color: #0b6f63;
  box-shadow: none;
}

.practice-panel .btn-outline {
  background: rgba(255, 255, 255, 0.12);
  border-color: rgba(255, 255, 255, 0.46);
  color: #fff;
}

.practice-stats {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(min(100%, 7.5rem), 1fr));
  gap: 0.55rem;
}

.practice-stat {
  border: 1px solid rgba(255, 255, 255, 0.28);
  border-radius: 12px;
  padding: 0.8rem;
  background: rgba(255, 255, 255, 0.12);
  text-align: center;
  box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.12);
  -webkit-backdrop-filter: blur(6px);
  backdrop-filter: blur(6px);
  margin: 0;
}

.practice-stat dd {
  display: block;
  font-family: 'DM Mono', monospace;
  font-size: 1.9rem;
  line-height: 1;
  margin: 0;
}

.practice-stat dt {
  display: block;
  margin-top: 0.3rem;
  font-size: 0.72rem;
  opacity: 0.88;
}

.practice-stat--sets {
  display: flex;
  justify-content: space-around;
  align-items: center;
  gap: 0.25rem;
}

.practice-stat--sets > div {
  display: flex;
  flex-direction: column;
  align-items: center;
  flex: 1;
}

.practice-stat--sets > div + div {
  border-left: 1px solid rgba(255, 255, 255, 0.2);
}

.unit-card-topline {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  flex-wrap: wrap;
  margin-bottom: 0.75rem;
}

.unit-quick-links {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  margin-top: 0.75rem;
}

.unit-quick-links a {
  display: inline-flex;
  align-items: center;
  color: var(--accent2);
  background: #fff;
  border: 1px solid var(--border);
  border-radius: 999px;
  padding: 0.4rem 0.75rem;
  font-size: 0.82rem;
  font-weight: 650;
}

.unit-quick-links a:hover {
  background: #f0fdfa;
  text-decoration: none;
}

@media (max-width: 780px) {
  .home-hero,
  .practice-panel {
    grid-template-columns: 1fr;
  }

  .home-hero {
    gap: 1rem;
    padding-top: 1.5rem;
  }

  .home-hero h1 {
    max-width: 12.5ch;
    font-size: clamp(2.4rem, 8.15vw, 3.85rem);
    line-height: 0.99;
    text-wrap: balance;
  }

  .hero-visual {
    min-height: 285px;
    justify-self: stretch;
    width: 100%;
  }

  .practice-stats {
    grid-template-columns: 1fr;
    gap: 0.35rem;
    background: rgba(255, 255, 255, 0.08);
    border: 1px solid rgba(255, 255, 255, 0.14);
    border-radius: 14px;
    padding: 0.35rem;
  }

  .practice-stat {
    display: flex;
    align-items: baseline;
    justify-content: space-between;
    gap: 0.75rem;
    text-align: left;
    padding: 0.8rem 0.9rem;
    min-height: 0;
    border: none;
    border-radius: 10px;
    background: rgba(255, 255, 255, 0.08);
    box-shadow: none;
    -webkit-backdrop-filter: none;
    backdrop-filter: none;
  }

  .practice-stat dd {
    font-size: 1.45rem;
    flex-shrink: 0;
  }

  .practice-stat dt {
    margin-top: 0;
    font-size: 0.8rem;
    text-align: right;
  }

  .practice-stat--sets {
    flex-direction: column;
    gap: 0.5rem;
  }

  .practice-stat--sets > div {
    flex-direction: row;
    justify-content: space-between;
    width: 100%;
    padding: 0.1rem 0;
  }

  .practice-stat--sets > div + div {
    border-left: none;
    border-top: 1px solid rgba(255, 255, 255, 0.2);
  }

  .practice-stat--sets dt {
    text-align: left;
    margin-top: 0;
  }
}

@media (min-width: 781px) and (max-width: 1360px) {
  .home-hero {
    grid-template-columns: minmax(0, 1.22fr) minmax(280px, 0.78fr);
    gap: clamp(1.35rem, 2.5vw, 2rem);
    align-items: center;
    padding: 0.5rem 0 1.35rem;
  }

  .home-hero h1 {
    max-width: 15.2ch;
    font-size: clamp(2.85rem, 3.8vw, 4rem);
    line-height: 0.98;
  }

  .hero-subtitle {
    max-width: 56ch;
  }

  .hero-visual {
    min-height: 305px;
    margin-top: 0;
  }
}

@media (max-width: 560px) {
  .container {
    width: min(var(--container), calc(100% - 1.25rem));
  }

  .hero-actions .btn,
  .practice-actions .btn,
  .unit-quick-links a {
    width: 100%;
    justify-content: center;
  }

  .hero-visual {
    display: none;
  }
}

@media (max-width: 480px) {
  /* Safety PPE cards: always single column on small phones */
  .safety-ppe-grid {
    grid-template-columns: 1fr;
  }

  /* Tabs: stack icon above label to avoid horizontal overflow inside each tab */
  .tab-btn.tab-rich {
    flex-direction: column;
    gap: 0.15rem;
    min-height: 56px;
    padding: 0.5rem 0.2rem;
  }

  .tab-icon {
    width: 1.45rem;
    height: 1.45rem;
    font-size: 0.72rem;
  }

  .tab-label {
    font-size: 0.73rem;
    line-height: 1.2;
  }
}

/* ===================== BLOG / STUDY SKILLS POSTS ===================== */

/* ── Shared structural styles ── */
.post-hero {
  border-radius: 18px;
  padding: 2rem 2rem 1.75rem;
  margin: 0 0 2rem 0;
}
.post-eyebrow {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  font-size: 0.75rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.13em;
  margin-bottom: 0.85rem;
}
.post-hero h1 {
  font-size: clamp(1.6rem, 3.5vw, 2.4rem);
  margin-bottom: 0.75rem;
  line-height: 1.12;
}
.post-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 0.6rem 1.25rem;
  font-size: 0.82rem;
  color: var(--muted);
  margin-top: 1rem;
}
.post-body { max-width: 720px; }
.post-body p {
  font-size: 1.02rem;
  line-height: 1.8;
  color: var(--dim);
  margin: 0 0 1.25rem 0;
}
.post-body h2 {
  font-size: 1.35rem;
  margin: 2rem 0 0.75rem;
  color: var(--text);
}
.post-body h3 {
  font-size: 1.08rem;
  margin: 1.5rem 0 0.5rem;
  color: var(--text);
}
.research-callout {
  border-radius: 0 10px 10px 0;
  padding: 1rem 1.25rem;
  margin: 1.5rem 0;
  font-size: 0.92rem;
  color: var(--dim);
  line-height: 1.7;
}
.research-callout .label {
  font-size: 0.72rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  margin-bottom: 0.4rem;
}
.myth-truth {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1rem;
  margin: 1.5rem 0;
}
@media (max-width: 600px) {
  .myth-truth { grid-template-columns: 1fr; }
}
.myth-box,
.truth-box {
  border-radius: var(--radius-md);
  padding: 1rem 1.25rem;
  font-size: 0.92rem;
  line-height: 1.7;
  color: var(--dim);
}
.myth-box {
  background: #fff1f2;
  border: 1px solid #fecdd3;
}
.myth-box .label {
  font-size: 0.72rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  margin-bottom: 0.4rem;
  color: #be123c;
}
.truth-box {
  background: #f0fdf4;
  border: 1px solid #bbf7d0;
}
.truth-box .label {
  font-size: 0.72rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  margin-bottom: 0.4rem;
  color: #15803d;
}
.strategy-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  padding: 1.35rem 1.5rem;
  margin: 1.25rem 0;
  box-shadow: var(--shadow-sm);
}
.strategy-card .strategy-num {
  font-size: 0.72rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  margin-bottom: 0.45rem;
}
.strategy-card h3 { margin: 0 0 0.6rem 0; font-size: 1.1rem; }
.strategy-card p {
  margin: 0;
  font-size: 0.97rem;
  line-height: 1.75;
  color: var(--dim);
}
.back-link {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  font-size: 0.85rem;
  color: var(--accent2);
  text-decoration: none;
  margin-bottom: 1.25rem;
  font-weight: 500;
  opacity: 0.8;
  transition: opacity 0.15s;
}
.back-link:hover { opacity: 1; text-decoration: none; }

/* ── Purple theme (body.post-purple) ── */
body.post-purple .post-hero {
  background: linear-gradient(135deg, rgba(124,58,237,0.09) 0%, rgba(124,58,237,0.03) 100%);
  border: 1px solid rgba(124,58,237,0.20);
}
body.post-purple .post-eyebrow { color: #7c3aed; }
body.post-purple .research-callout {
  background: #f5f3ff;
  border-left: 3px solid #7c3aed;
}
body.post-purple .research-callout .label { color: #7c3aed; }
body.post-purple .strategy-card .strategy-num { color: #7c3aed; }
body.post-purple .making-step .step-label { color: #7c3aed; }
body.post-purple .game-steps li::before { color: #7c3aed; background: #ede9fe; }

/* ── Green theme (body.post-green) ── */
body.post-green .post-hero {
  background: linear-gradient(135deg, rgba(5,150,105,0.10) 0%, rgba(5,150,105,0.03) 100%);
  border: 1px solid rgba(5,150,105,0.22);
}
body.post-green .post-eyebrow { color: var(--green); }
body.post-green .research-callout {
  background: #ecfdf5;
  border-left: 3px solid var(--green);
}
body.post-green .research-callout .label { color: var(--green); }
body.post-green .strategy-card .strategy-num { color: var(--green); }

/* ── Blue theme (body.post-blue) ── */
body.post-blue .post-hero {
  background: linear-gradient(135deg, rgba(29,78,216,0.09) 0%, rgba(29,78,216,0.03) 100%);
  border: 1px solid rgba(29,78,216,0.18);
}
body.post-blue .post-eyebrow { color: #1d4ed8; }
body.post-blue .research-callout {
  background: #eff6ff;
  border-left: 3px solid #1d4ed8;
}
body.post-blue .research-callout .label { color: #1d4ed8; }
body.post-blue .strategy-card .strategy-num { color: #1d4ed8; }
body.post-blue .making-step .step-label { color: #1d4ed8; }
body.post-blue .game-steps li::before { color: #1d4ed8; background: #dbeafe; }

/* ── Flashcard-page components ── */
.game-card {
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  padding: 1.5rem;
  margin: 1.25rem 0;
}
.game-card-header {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  margin-bottom: 1rem;
}
.game-badge {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 36px;
  height: 36px;
  border-radius: 50%;
  background: linear-gradient(135deg, #7c3aed, #6d28d9);
  color: #fff;
  font-weight: 700;
  font-size: 0.88rem;
  flex-shrink: 0;
}
.game-name {
  font-weight: 700;
  font-size: 1.05rem;
  color: var(--text);
}
.game-tag {
  margin-left: auto;
  font-size: 0.7rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  background: #ede9fe;
  color: #5b21b6;
  padding: 0.2rem 0.5rem;
  border-radius: 999px;
  flex-shrink: 0;
}
.game-steps {
  counter-reset: game-step;
  list-style: none;
  margin: 0;
  padding: 0;
}
.game-steps li {
  counter-increment: game-step;
  display: grid;
  grid-template-columns: 24px 1fr;
  gap: 0.6rem;
  padding: 0.5rem 0;
  border-top: 1px solid rgba(219,228,238,0.7);
  font-size: 0.92rem;
  line-height: 1.65;
  color: var(--dim);
  align-items: start;
}
.game-steps li:first-child { border-top: none; }
.game-steps li::before {
  content: counter(game-step);
  font-size: 0.72rem;
  font-weight: 600;
  border-radius: 999px;
  width: 20px;
  height: 20px;
  display: flex;
  align-items: center;
  justify-content: center;
  margin-top: 0.2rem;
  flex-shrink: 0;
}
.making-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.75rem;
  margin: 1.5rem 0;
}
.making-step {
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 1rem 1.1rem;
}
.making-step .step-label {
  font-size: 0.7rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  margin-bottom: 0.4rem;
}
.making-step p {
  font-size: 0.88rem;
  line-height: 1.6;
  color: var(--dim);
  margin: 0;
}
.flashcard-example { margin: 1.5rem 0; }
.fc-inner {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.75rem;
}
.fc-face {
  border-radius: var(--radius-sm);
  padding: 1.25rem 1.35rem;
  text-align: center;
  font-size: 0.92rem;
  line-height: 1.6;
}
.fc-front {
  background: #f0fdfa;
  border: 2px solid #99f6e4;
  color: var(--text);
}
.fc-back {
  background: #ecfdf5;
  border: 2px solid #bbf7d0;
  color: var(--dim);
}
.fc-label {
  font-size: 0.68rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  margin-bottom: 0.5rem;
  display: block;
}
.fc-front .fc-label { color: var(--accent2); }
.fc-back .fc-label { color: var(--green); }

/* ── Flashcard Connection example ── */
.ce-intro {
  font-size: 0.78rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.09em;
  color: var(--muted);
  margin: 0 0 0.75rem;
}
.connection-pair {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  margin-bottom: 1.25rem;
}
.pulled-card {
  flex: 1;
  background: #fff;
  border: 1.5px solid var(--border);
  border-radius: 10px;
  padding: 1rem;
  text-align: center;
  font-size: 0.97rem;
  font-weight: 700;
  color: var(--text);
  min-width: 0;
}
.connection-arrow {
  font-size: 1.1rem;
  color: var(--muted);
  flex-shrink: 0;
  -webkit-user-select: none;
  user-select: none;
}
.connection-written {
  background: #faf9ff;
  border: 1.5px dashed #c4b5fd;
  border-radius: var(--radius-sm);
  padding: 0.9rem 1rem;
  font-size: 0.9rem;
  line-height: 1.75;
  color: #374151;
}
.connection-written .cw-label {
  font-size: 0.65rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: #7c3aed;
  margin-bottom: 0.45rem;
  display: block;
}

/* ── Prev / Next post navigation (shared) ── */
.prev-post,
.next-post {
  background: linear-gradient(135deg, #064e3b 0%, #0b6f63 100%);
  border-radius: var(--radius-lg);
  padding: 1.6rem 2rem;
  margin-top: 2.5rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1.5rem;
}
.prev-post-label,
.next-post-label {
  font-size: 0.72rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  color: rgba(255,255,255,0.6);
  margin-bottom: 0.35rem;
}
.prev-post-title,
.next-post-title { font-size: 1.05rem; font-weight: 700; color: #fff; line-height: 1.3; }
.prev-post-btn,
.next-post-btn {
  background: #fff;
  color: var(--accent2);
  font-weight: 700;
  font-size: 0.9rem;
  padding: 0.7rem 1.4rem;
  border-radius: 10px;
  text-decoration: none;
  white-space: nowrap;
  flex-shrink: 0;
  transition: transform 0.15s;
}
.prev-post-btn:hover,
.next-post-btn:hover { transform: translateY(-1px); text-decoration: none; color: var(--accent2); }

/* ── Practice-tests-page components ── */
.effect-comparison {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.75rem;
  margin: 1.5rem 0;
}
.effect-low, .effect-high {
  border-radius: var(--radius-sm);
  padding: 1rem 1.1rem;
  font-size: 0.88rem;
  line-height: 1.65;
}
.effect-low {
  background: #fef2f2;
  border: 1px solid #fecaca;
}
.effect-high {
  background: #ecfdf5;
  border: 1px solid #bbf7d0;
}
.effect-low .label { color: #991b1b; font-size: 0.7rem; font-weight: 700; text-transform: uppercase; letter-spacing: 0.1em; margin-bottom: 0.4rem; }
.effect-high .label { color: #166534; font-size: 0.7rem; font-weight: 700; text-transform: uppercase; letter-spacing: 0.1em; margin-bottom: 0.4rem; }
.effect-low ul, .effect-high ul { margin: 0.3rem 0 0 1.1rem; padding: 0; color: var(--dim); }
.effect-low li, .effect-high li { margin-bottom: 0.25rem; }
.effect-low p, .effect-high p { margin: 0.3rem 0 0; color: var(--dim); }

/* ── Subscription success page ── */
@keyframes spin { to { transform: rotate(360deg); } }
.subscription-success { max-width: 560px; text-align: center; padding-top: 5rem; }
.subscription-success .state-icon { font-size: 2.5rem; margin-bottom: 1rem; }
.subscription-success h1 { font-size: 1.6rem; margin-bottom: 0.5rem; }
.subscription-success .subtitle { margin: 0 0 2rem; }
.subscription-success .spinner-row {
  display: flex; align-items: center; justify-content: center;
  gap: 0.75rem; color: var(--muted); font-size: 0.93rem;
}
#spinner {
  width: 18px; height: 18px;
  border: 2px solid #dbe4ee; border-top-color: #0f766e;
  border-radius: 50%; animation: spin 0.8s linear infinite;
}
#state-error { display: none; }
.subscription-success h2 { margin-bottom: 0.5rem; }
.subscription-success .error-subtitle { color: var(--muted); margin-bottom: 1.5rem; }

/* ── Unit 10: Chemical Bonding ── */

/* Lewis symbol size variants */
.lewis-box--170-210 { min-width: 170px; max-width: 210px; }
.lewis-box--180-220 { min-width: 180px; max-width: 220px; }
.lewis-box--190-230 { min-width: 190px; max-width: 230px; }
.lewis-box--200-240 { min-width: 200px; max-width: 240px; }

.bond-tool-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 0.8rem;
  margin-top: 0.8rem;
}
.bond-tool-panel {
  background: rgba(255,255,255,0.78);
  border: 1px solid var(--border-slate);
  border-radius: 16px;
  padding: 0.9rem 1rem;
}
.bond-tool-panel h4 { margin: 0 0 0.45rem; font-size: 0.92rem; color: #0f172a; }
.bond-tool-panel p  { margin: 0; color: #334155; line-height: 1.55; font-size: 0.92rem; }

/* VSEPR Explorer */
.vsepr-tool {
  margin-top: 1rem;
  display: grid;
  gap: 0.9rem;
}

.vsepr-tool.tool-visual-panel {
  padding: 1rem;
}

.vsepr-controls,
.vsepr-visual {
  background: rgba(255,255,255,0.82);
  border: 1px solid var(--border-slate);
  border-radius: 18px;
  padding: 1rem;
}
.vsepr-kicker {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  border-radius: 999px;
  padding: 0.35rem 0.7rem;
  background: #f0fdfa;
  color: #0b6f63;
  font-size: 0.76rem;
  font-weight: 800;
  letter-spacing: 0.04em;
  text-transform: uppercase;
}
.vsepr-controls h3,
.vsepr-visual h3 { margin: 0.65rem 0 0.35rem; font-size: 1.05rem; color: #0f172a; }
.vsepr-intro,
.vsepr-helper,
.vsepr-caption { color: #475569; line-height: 1.55; font-size: 0.92rem; }
.vsepr-helper {
  margin: 0;
  padding: 0.8rem 0.9rem;
  border-radius: 14px;
  background: #f8fafc;
  border: 1px solid rgba(148, 163, 184, 0.18);
}
.vsepr-selectors { display: grid; gap: 0.85rem; margin-top: 0.95rem; }
.vsepr-selectors label { display: block; margin-bottom: 0.35rem; font-weight: 700; color: #0f172a; }
.vsepr-selectors select { width: 100%; }
.vsepr-visual-top {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  gap: 0.75rem;
  flex-wrap: wrap;
}
.vsepr-badges { display: flex; flex-wrap: wrap; gap: 0.45rem; margin: 0.8rem 0 0.95rem; }
.vsepr-badge {
  display: inline-flex;
  align-items: center;
  border-radius: 999px;
  padding: 0.38rem 0.75rem;
  background: #f0fdfa;
  color: #064e3b;
  font-size: 0.82rem;
  font-weight: 700;
}
.vsepr-diagram-shell {
  border-radius: 18px;
  background:
    radial-gradient(circle at top, rgba(219, 234, 254, 0.85), rgba(239, 246, 255, 0.65) 38%, rgba(248, 250, 252, 0.95) 100%);
  border: 1px solid var(--border-slate);
  padding: 0.85rem;
  max-width: 260px;
  margin-inline: auto;
}
.vsepr-diagram { min-height: 0; }
.vsepr-diagram svg { width: 100%; height: auto; display: block; }
.vsepr-out {
  margin-top: 0;
  padding: 0.95rem 1rem;
  border-radius: 16px;
  background: #f8fafc;
  border: 1px solid rgba(148, 163, 184, 0.18);
}
.vsepr-shape-name,
.vsepr-eg-name  { color: #0f172a; font-weight: 800; }
.vsepr-eg-name  { margin-top: 0.3rem; }
.vsepr-details  { margin-top: 0.65rem; color: #334155; line-height: 1.6; }

/* Geometry grid (section 10.6 reference cards) */
.geo-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 1rem;
  align-items: start;
  margin-top: 1rem;
}
.geo-card {
  background: rgba(255,255,255,0.82);
  border: 1px solid var(--border-slate);
  border-radius: 18px;
  padding: 1rem;
  display: flex;
  flex-direction: column;
  align-items: center;
  text-align: center;
  min-height: 100%;
}
.gc-name    { color: #0f172a; font-size: 1rem; font-weight: 800; }
.gc-formula { margin-top: 0.22rem; color: #0b6f63; font-size: 0.84rem; font-weight: 700; }
.geo-card svg { width: min(100%, 160px); height: auto; margin: 0.7rem auto 0.25rem; display: block; }
.gc-angle   { color: #0f172a; font-weight: 700; }
.gc-example { margin-top: 0.3rem; color: #475569; font-size: 0.92rem; line-height: 1.5; }

/* Lewis diagram grid (sections 10.2 and 10.4) — grid/250px layout wins */
.lewis-diagram {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(min(220px, 100%), 1fr));
  gap: 24px;
  justify-content: center;
  margin: 32px auto;
  max-width: 900px;
  align-items: stretch;
}
.lewis-box {
  border: 1px solid #cbd5e1;
  border-radius: 8px;
  padding: clamp(14px, 3vw, 20px);
  background-color: #ffffff;
  box-shadow: 0 2px 4px rgba(0, 0, 0, 0.05);
  text-align: center;
  width: 100%;
  max-width: 210px;
  min-height: 200px;
  height: auto;
  display: grid;
  grid-template-rows: auto 1fr auto;
  align-items: center;
  justify-items: center;
  justify-self: center;
  overflow: visible;
}
.lewis-box svg {
  display: block;
  width: min(100%, 160px);
  height: auto;
  margin-inline: auto;
  overflow: visible;
}
.lb-name    { font-weight: 600; color: #334155; margin-bottom: 12px; }
.lb-formula { font-size: 0.8rem; color: #64748b; margin-top: 12px; line-height: 1.4; }

/* NASBU steps (modeled after .steps / .step / .step-num / .step-content) */
.nasbu-steps {
  display: flex;
  flex-direction: column;
  gap: 0;
  margin: 1.25rem 0;
}
.nasbu-row {
  display: flex;
  gap: 1rem;
  align-items: flex-start;
  padding: 1rem 0;
  border-bottom: 1px solid rgba(148,163,184,0.18);
}
.nasbu-row:last-child { border-bottom: none; }
.nasbu-letter {
  flex-shrink: 0;
  width: 2.4rem;
  height: 2.4rem;
  border-radius: 50%;
  background: #0f766e;
  color: #fff;
  font-size: 1.15rem;
  font-weight: 800;
  display: flex;
  align-items: center;
  justify-content: center;
  letter-spacing: 0.02em;
  margin-top: 0.1rem;
}
.nasbu-content { flex: 1; color: #334155; line-height: 1.65; }
.nasbu-content p { margin: 0.35rem 0 0; }

/* Responsive adjustments */
@media (max-width: 980px) {
  .geo-grid { grid-template-columns: 1fr; }
}
/* ===================== STUDY SKILLS BLOG PAGE ===================== */
.blog-hero {
  padding: 2rem 0 1.75rem;
  max-width: 680px;
}

.blog-hero-eyebrow {
  font-size: 0.72rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  color: var(--accent);
  margin-bottom: 0.85rem;
}

.blog-hero h1 {
  font-size: clamp(1.9rem, 5vw, 2.9rem);
  font-weight: 800;
  line-height: 1.1;
  color: var(--text);
  margin: 0 0 1rem;
  letter-spacing: -0.02em;
}

.blog-hero-sub {
  font-size: 1rem;
  line-height: 1.75;
  color: var(--dim);
  margin: 0;
  max-width: 600px;
}

/* Author / about card */
.author-card {
  background: rgba(255, 255, 255, 0.72);
  border: 1px solid var(--border);
  border-left: 4px solid var(--accent);
  border-radius: var(--radius-md);
  padding: 1.25rem 1.5rem;
  margin: 0.5rem 0 2rem;
  -webkit-backdrop-filter: blur(4px);
  backdrop-filter: blur(4px);
}

.author-card h3 {
  font-size: 0.78rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--accent);
  margin: 0 0 0.55rem;
}

.author-card p {
  font-size: 0.9rem;
  line-height: 1.75;
  color: var(--dim);
  margin: 0;
}

/* Post grid */
.post-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1rem;
  margin-bottom: 1.5rem;
}

/* Post cards */
.post-card {
  display: flex;
  flex-direction: column;
  text-decoration: none;
  color: inherit;
  background: var(--white-88);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  padding: 1.4rem 1.5rem 1.25rem;
  transition: transform 0.18s ease, box-shadow 0.18s ease;
  box-shadow: var(--shadow-sm);
  position: relative;
  overflow: hidden;
}

.post-card::before {
  content: '';
  position: absolute;
  top: 0; left: 0; right: 0;
  height: 3px;
  background: var(--accent);
}

.post-card[data-color="blue"]::before   { background: var(--accent2); }
.post-card[data-color="green"]::before  { background: var(--green); }
.post-card[data-color="purple"]::before { background: var(--violet); }

.post-card:hover {
  transform: translateY(-3px);
  box-shadow: var(--shadow-md);
  text-decoration: none;
  color: inherit;
}

.post-card-num {
  font-size: 2rem;
  font-weight: 800;
  line-height: 1;
  letter-spacing: -0.03em;
  margin-bottom: 0.65rem;
  color: rgba(15, 138, 122, 0.15);
}

.post-card[data-color="blue"]   .post-card-num { color: rgba(11, 111, 99, 0.18); }
.post-card[data-color="green"]  .post-card-num { color: rgba(33, 134, 95, 0.2); }
.post-card[data-color="purple"] .post-card-num { color: rgba(124, 92, 196, 0.2); }

.post-card-content {
  display: flex;
  flex-direction: column;
  gap: 0.45rem;
  flex: 1;
}

.post-card-eyebrow {
  font-size: 0.68rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--muted);
}

.post-card[data-color="blue"]   .post-card-eyebrow { color: var(--accent2); }
.post-card[data-color="green"]  .post-card-eyebrow { color: var(--green); }
.post-card[data-color="purple"] .post-card-eyebrow { color: var(--violet); }

.post-card h2 {
  font-size: 1.05rem;
  font-weight: 750;
  line-height: 1.3;
  color: var(--text);
  margin: 0;
}

.post-card-desc {
  font-size: 0.83rem;
  line-height: 1.65;
  color: var(--dim);
  margin: 0;
  flex: 1;
}

.post-card-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 0.3rem 0.65rem;
  margin-top: 0.4rem;
}

.post-card-meta span {
  font-size: 0.67rem;
  font-weight: 600;
  color: var(--muted);
  letter-spacing: 0.02em;
}

.post-card-cta {
  font-size: 0.82rem;
  font-weight: 700;
  color: var(--accent);
  margin-top: 0.85rem;
}

.post-card[data-color="blue"]   .post-card-cta { color: var(--accent2); }
.post-card[data-color="green"]  .post-card-cta { color: var(--green); }
.post-card[data-color="purple"] .post-card-cta { color: var(--violet); }

/* Coming soon placeholder cards */
.post-card-soon {
  background: rgba(255, 255, 255, 0.45);
  border: 1.5px dashed var(--border-strong, #d9c8b4);
  border-radius: var(--radius-md);
  padding: 1.4rem 1.5rem;
  color: var(--muted);
  font-size: 0.87rem;
  line-height: 1.55;
  display: flex;
  flex-direction: column;
  gap: 0.55rem;
}

.soon-label {
  font-size: 0.64rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  color: var(--gold, #b7791f);
  background: rgba(183, 121, 31, 0.1);
  padding: 0.18rem 0.55rem;
  border-radius: 99px;
  align-self: flex-start;
}

/* Mobile: single column */
@media (max-width: 680px) {
  .post-grid {
    grid-template-columns: 1fr;
  }

  .blog-hero {
    padding: 1.25rem 0 1.25rem;
  }

  .author-card {
    margin-bottom: 1.5rem;
  }
}

/* ===================== PRACTICE HUB PAGE ===================== */

/* Access summary callout */
.access-summary {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 1.25rem;
  background: rgba(15, 138, 122, 0.06);
  border: 1px solid rgba(15, 138, 122, 0.2);
  border-left: 4px solid var(--accent);
  border-radius: var(--radius-md);
  padding: 1.25rem 1.5rem;
  margin-bottom: 1.75rem;
}

.access-summary-text { flex: 1; }

.access-summary-title {
  font-weight: 700;
  color: var(--text);
  margin-bottom: 0.3rem;
}

.access-summary-desc {
  font-size: 0.9rem;
  color: var(--dim);
  line-height: 1.65;
}

.access-summary-note {
  font-family: 'DM Mono', monospace;
  font-size: 0.72rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--accent2);
  background: rgba(15, 138, 122, 0.1);
  padding: 0.3rem 0.75rem;
  border-radius: 99px;
  white-space: nowrap;
  align-self: flex-start;
}

/* Stats strip */
.stats-strip {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 0.75rem;
  margin-bottom: 1.75rem;
}

.stat-tile {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  padding: 1.25rem 1.5rem;
  text-align: center;
  box-shadow: var(--shadow-sm);
}

.stat-num {
  font-size: 2.25rem;
  font-weight: 800;
  color: var(--accent2);
  line-height: 1.1;
  margin-bottom: 0.3rem;
  font-variant-numeric: tabular-nums;
}

.stat-tile .stat-label {
  font-size: 0.78rem;
  font-weight: 500;
  color: var(--muted);
  text-transform: uppercase;
  letter-spacing: 0.07em;
  margin-top: 0;
}

/* How-it-works steps */
.how-it-works {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 0.75rem;
  margin-bottom: 2.5rem;
}

.how-step {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 1rem 1.1rem;
}

.how-step-num {
  font-family: 'DM Mono', monospace;
  font-size: 0.7rem;
  font-weight: 700;
  color: var(--accent);
  letter-spacing: 0.05em;
}

.how-step-text {
  font-size: 0.88rem;
  color: var(--dim);
  line-height: 1.55;
}

/* Section headers */
.section-eyebrow {
  font-size: 0.7rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  color: var(--accent2);
  margin-bottom: 0.25rem;
}

.section-heading {
  font-size: 1.5rem;
  font-weight: 750;
  color: var(--text);
  margin: 0 0 0.5rem;
  line-height: 1.2;
}

.section-desc {
  font-size: 0.92rem;
  color: var(--dim);
  line-height: 1.65;
  margin-bottom: 1.5rem;
  max-width: 640px;
}

.section-desc-wide {
  max-width: 980px;
}

/* Practice unit grid */
.practice-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 0.9rem;
  margin-bottom: 2.5rem;
}

.practice-card {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
  text-decoration: none;
  background: var(--surface);
  border: 1px solid var(--border);
  border-left: 3px solid rgba(15, 138, 122, 0.3);
  border-radius: var(--radius-md);
  padding: 1.25rem 1.35rem;
  color: var(--text);
  box-shadow: var(--shadow-sm);
  transition: border-color 0.18s, box-shadow 0.18s, transform 0.18s, background 0.18s;
}

.practice-card:hover,
.practice-card:focus-visible {
  border-left-color: var(--accent);
  border-color: rgba(15, 138, 122, 0.35);
  background: rgba(15, 138, 122, 0.03);
  transform: translateY(-2px);
  box-shadow: 0 8px 24px rgba(15, 138, 122, 0.12);
  text-decoration: none;
  outline: none;
}

.practice-card-top {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.5rem;
}

.practice-unit-num {
  font-family: 'DM Mono', monospace;
  font-size: 0.7rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--accent2);
}

.practice-problem-count {
  font-family: 'DM Mono', monospace;
  font-size: 0.68rem;
  font-weight: 600;
  color: var(--muted);
}

.practice-card-setsizes {
  font-family: 'DM Mono', monospace;
  font-size: 0.68rem;
  font-weight: 600;
  color: var(--muted);
  letter-spacing: 0.01em;
}

.practice-card-title {
  font-size: 1rem;
  font-weight: 700;
  color: var(--text);
  line-height: 1.3;
}

.practice-card-blurb {
  font-size: 0.83rem;
  color: var(--dim);
  line-height: 1.55;
  flex: 1;
}

.practice-card-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 0.35rem;
  margin-top: 0.25rem;
}

.meta-pill {
  display: inline-block;
  font-size: 0.65rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.07em;
  padding: 0.18rem 0.55rem;
  border-radius: 99px;
  border: 1px solid transparent;
}

.pill-calc {
  background: rgba(15, 118, 110, 0.08);
  color: #065f54;
  border-color: rgba(15, 118, 110, 0.18);
}

.pill-concept {
  background: var(--accent-8);
  color: var(--accent2);
  border-color: rgba(15, 138, 122, 0.2);
}

.pill-multi {
  background: rgba(124, 92, 196, 0.08);
  color: #6d4bbf;
  border-color: rgba(124, 92, 196, 0.18);
}

.practice-card-cta {
  font-size: 0.82rem;
  font-weight: 600;
  color: var(--accent2);
  margin-top: 0.25rem;
  transition: color 0.18s;
}

.practice-card:hover .practice-card-cta {
  color: var(--accent);
}

/* Bottom CTA banner */
.bottom-cta {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1.5rem;
  background: rgba(15, 138, 122, 0.05);
  border: 1px solid var(--accent-18);
  border-radius: var(--radius-lg);
  padding: 1.75rem 2rem;
  margin-bottom: 2rem;
  flex-wrap: wrap;
}

.bottom-cta-text { flex: 1 1 300px; }

.bottom-cta-title {
  font-size: 1.1rem;
  font-weight: 700;
  color: var(--text);
  margin-bottom: 0.35rem;
}

.bottom-cta-desc {
  font-size: 0.88rem;
  color: var(--dim);
  line-height: 1.65;
}

/* Practice hub responsive */
@media (max-width: 900px) {
  .practice-grid   { grid-template-columns: repeat(2, 1fr); }
  .how-it-works    { grid-template-columns: repeat(2, 1fr); }
}

@media (max-width: 600px) {
  .practice-grid   { grid-template-columns: 1fr; }
  .how-it-works    { grid-template-columns: 1fr; }
  .stats-strip     { gap: 0.5rem; }
  .stat-num        { font-size: 1.75rem; }
  .access-summary  { flex-direction: column; }
  .bottom-cta      { flex-direction: column; align-items: flex-start; }
}
.home-brand {
  margin-bottom: 1.25rem;
}


/* ═══════════════════════════════════════════
   Per-page inline styles (moved from HTML)
═══════════════════════════════════════════ */

/* ── 04_Learn_Electron_Configuration.html ── */
/* ── Orbital box diagrams ── */
.orbital-row {
  display: flex;
  align-items: center;
  gap: 0.4rem;
  flex-wrap: wrap;
  margin: 0.5rem 0;
}
.page-04-learn-electron-configuration .orb-box {
  width: 38px;
  height: 38px;
  border: 2px solid var(--border);
  border-radius: 6px;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 2px;
  background: #fff;
  font-size: 1rem;
}
.page-04-learn-electron-configuration .orb-box.full { border-color: #93c5fd; background: #eff6ff; }
.page-04-learn-electron-configuration .orb-box.up-only { border-color: #a7f3d0; background: #ecfdf5; }
.page-04-learn-electron-configuration .orb-box.empty { border-color: var(--border); background: #f8fafc; }
.arrow-up-el { color: #1d4ed8; font-size: 1rem; line-height: 1; }
.arrow-down-el { color: #0f766e; font-size: 1rem; line-height: 1; }
.sublevel-name {
  font-family: 'DM Mono', monospace;
  font-size: 0.82rem;
  color: var(--dim);
  min-width: 2.2rem;
  font-weight: 500;
}

/* ── Spectrum bar ── */
.spectrum-bar {
  height: 18px;
  border-radius: 6px;
  margin: 0.75rem 0 0.35rem;
  background: linear-gradient(to right, #7c3aed, #2563eb, #0891b2, #059669, #ca8a04, #ea580c, #dc2626);
}
.spectrum-labels {
  display: flex;
  justify-content: space-between;
  font-size: 0.75rem;
  color: var(--muted);
  margin-bottom: 0.5rem;
}

.em-spectrum-card {
  margin: 1rem 0 1.1rem;
  padding: 1rem 1rem 1.1rem;
  border: 1px solid #cfe7e0;
  border-radius: 18px;
  background:
    radial-gradient(circle at top left, rgba(255, 255, 255, 0.95), rgba(243, 251, 247, 0.92)),
    linear-gradient(180deg, rgba(232, 245, 239, 0.55), rgba(255, 255, 255, 0.98));
  box-shadow: 0 14px 30px rgba(21, 94, 76, 0.08);
}

.em-spectrum-topline,
.em-spectrum-scale,
.visible-spectrum-direction,
.visible-spectrum-head {
  display: flex;
  justify-content: space-between;
  gap: 0.75rem;
}

.em-spectrum-topline,
.em-spectrum-scale,
.visible-spectrum-direction {
  font-size: 0.76rem;
  color: var(--muted);
}

.em-spectrum-topline {
  margin-bottom: 0.45rem;
  font-weight: 600;
}

.em-spectrum-band,
.visible-spectrum-bar {
  display: grid;
  overflow: hidden;
  border-radius: 14px;
}

.em-spectrum-band {
  grid-template-columns: 1fr 1fr 1.1fr 0.7fr 1.1fr 1.3fr 1.6fr;
  border: 1px solid rgba(15, 23, 42, 0.08);
}

.em-segment {
  min-height: 68px;
  padding: 0.8rem 0.4rem;
  display: flex;
  align-items: flex-end;
  justify-content: center;
  text-align: center;
  font-size: 0.77rem;
  line-height: 1.2;
  font-weight: 700;
  color: #fff;
}

.em-segment.gamma { background: #581c87; }
.em-segment.xray { background: #1d4ed8; }
.em-segment.uv { background: #0891b2; }
.em-segment.visible {
  background: linear-gradient(90deg, #6d28d9 0%, #2563eb 18%, #0891b2 35%, #16a34a 52%, #facc15 68%, #f97316 83%, #dc2626 100%);
  color: #1f2937;
  text-shadow: 0 1px 1px rgba(255, 255, 255, 0.35);
}
.em-segment.ir { background: #b45309; }
.em-segment.micro { background: #475569; }
.em-segment.radio { background: #1f2937; }

.em-spectrum-scale {
  margin-top: 0.45rem;
}

.em-spectrum-note {
  margin: 0.7rem 0 0;
  font-size: 0.92rem;
  color: #355b56;
}

.visible-spectrum-detail {
  margin-top: 1rem;
  padding-top: 0.95rem;
  border-top: 1px solid rgba(23, 79, 71, 0.12);
}

.visible-spectrum-head {
  align-items: baseline;
  margin-bottom: 0.55rem;
}

.visible-spectrum-head h3 {
  margin: 0;
  font-size: 1rem;
  color: #174f47;
}

.visible-spectrum-head span {
  font-size: 0.78rem;
  color: var(--muted);
}

.visible-spectrum-bar {
  grid-template-columns: 1fr 1.1fr 1.35fr 0.8fr 0.95fr 1.35fr;
  border: 1px solid rgba(15, 23, 42, 0.08);
}

.visible-color {
  min-height: 92px;
  padding: 0.85rem 0.45rem;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  gap: 0.5rem;
  text-align: center;
}

.visible-color strong {
  display: block;
  font-size: 0.82rem;
}

.visible-color span {
  font-size: 0.76rem;
  line-height: 1.2;
  font-weight: 600;
}

.visible-color.violet { background: #6d28d9; color: #f5f3ff; }
.visible-color.blue { background: #2563eb; color: #eff6ff; }
.visible-color.green { background: #16a34a; color: #ecfdf5; }
.visible-color.yellow { background: #fde047; color: #3f3300; }
.visible-color.orange { background: #fb923c; color: #4a2000; }
.visible-color.red { background: #dc2626; color: #fef2f2; }

.visible-spectrum-direction {
  margin-top: 0.45rem;
}

@media (max-width: 760px) {
  .em-spectrum-topline,
  .em-spectrum-scale,
  .visible-spectrum-direction,
  .visible-spectrum-head {
    flex-direction: column;
    align-items: flex-start;
    gap: 0.25rem;
  }

  .em-spectrum-band {
    grid-template-columns: repeat(7, minmax(70px, 1fr));
    overflow-x: auto;
  }

  .visible-spectrum-bar {
    grid-template-columns: repeat(6, minmax(92px, 1fr));
    overflow-x: auto;
  }

  .em-segment,
  .visible-color {
    min-height: 84px;
  }
}

/* ── Config builder output ── */
.config-result {
  margin-top: 1rem;
  padding: 1rem 1.1rem;
  background: #eff6ff;
  border: 1px solid #bfdbfe;
  border-radius: var(--radius-sm);
  font-family: 'DM Mono', monospace;
  font-size: 0.92rem;
  line-height: 1.75;
  color: #1e3a8a;
}
.config-label {
  display: block;
  font-size: 0.76rem;
  color: var(--accent2);
  text-transform: uppercase;
  letter-spacing: 0.1em;
  margin-bottom: 0.3rem;
  font-family: 'DM Mono', monospace;
}

/* ── Mini periodic table ── */
.pt-legend {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  margin: 0.75rem 0;
  font-size: 0.83rem;
  color: var(--dim);
}
.pt-swatch { display: flex; align-items: center; gap: 0.4rem; }
.pt-color { width: 18px; height: 18px; border-radius: 4px; flex-shrink: 0; }
.mini-pt-wrap { position: relative; margin-top: 0.5rem; overflow-x: auto; }
.mini-pt {
  display: grid;
  grid-template-columns: repeat(18, 34px);
  grid-template-rows: repeat(7, 30px);
  gap: 2px;
  width: max-content;
}
.mini-pt-f-wrap {
  display: flex;
  align-items: flex-start;
  gap: 0.4rem;
  margin-top: 6px;
  width: max-content;
}
.mini-pt-f-labels {
  display: flex;
  flex-direction: column;
  gap: 2px;
}
.mini-pt-f-label {
  height: 30px;
  display: flex;
  align-items: center;
  font-size: 0.6rem;
  color: var(--muted);
  padding-right: 2px;
}
.mini-pt-f {
  display: grid;
  grid-template-columns: repeat(15, 34px);
  grid-template-rows: repeat(2, 30px);
  gap: 2px;
}
.pt-cell {
  width: 34px;
  height: 30px;
  border-radius: 4px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.68rem;
  font-weight: 600;
  transition: 0.15s ease;
  -webkit-user-select: none;
  user-select: none;
}
.pt-cell.empty { background: transparent; }
.pt-cell.s-blk { background: #dbeafe; color: #1d4ed8; border: 1px solid #93c5fd; }
.pt-cell.p-blk { background: #d1fae5; color: #065f46; border: 1px solid #6ee7b7; }
.pt-cell.d-blk { background: #fef3c7; color: #78350f; border: 1px solid #fcd34d; }
.pt-cell.f-blk { background: #fce7f3; color: #831843; border: 1px solid #f9a8d4; }
.pt-cell:hover:not(.empty) { filter: brightness(0.92); transform: scale(1.1); z-index: 5; }
.page-04-learn-electron-configuration .pt-cell.selected { outline: 2px solid var(--accent2); outline-offset: 1px; }
.pt-tooltip {
  display: none;
  position: fixed;
  z-index: 100;
  background: #1e293b;
  color: #f1f5f9;
  padding: 0.5rem 0.75rem;
  border-radius: 8px;
  font-size: 0.8rem;
  line-height: 1.5;
  pointer-events: none;
  max-width: 240px;
  white-space: normal;
}

.challenge-prompt {
  padding: 1.15rem 1.15rem 1.2rem;
  border-radius: 18px;
  background:
    radial-gradient(circle at top right, rgba(255, 255, 255, 0.72), transparent 38%),
    linear-gradient(135deg, rgba(29, 78, 216, 0.18), rgba(14, 165, 233, 0.12));
  border: 1px solid rgba(37, 99, 235, 0.22);
  box-shadow: 0 12px 28px rgba(37, 99, 235, 0.08);
  margin-bottom: 1rem;
  position: relative;
  overflow: hidden;
}
.challenge-prompt::before {
  content: "";
  position: absolute;
  inset: 0 auto 0 0;
  width: 6px;
  background: linear-gradient(180deg, #1d4ed8, #0ea5e9);
}
.challenge-prompt strong {
  display: block;
  color: var(--text);
  margin-bottom: 0.45rem;
  font-size: 1.05rem;
}
.challenge-prompt p {
  margin: 0.25rem 0 0;
  color: #1e3a8a;
}
.challenge-prompt ol {
  margin: 0.7rem 0 0 1.1rem;
  padding: 0;
  color: var(--dim);
}
.challenge-prompt li {
  margin: 0.2rem 0;
}
.challenge-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 0.9rem 1rem;
}
.challenge-field {
  background: rgba(255, 255, 255, 0.72);
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 0.85rem 0.9rem;
}
.challenge-field h4,
.challenge-field .mini-label {
  margin: 0 0 0.45rem;
  font-size: 0.78rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--accent2);
}
.challenge-field p {
  margin: 0.25rem 0 0;
  font-size: 0.88rem;
  color: var(--muted);
}
.challenge-note {
  margin-top: 0.75rem;
  font-size: 0.86rem;
  color: var(--muted);
}
.orbital-input-row {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.45rem;
}
.page-04-learn-electron-configuration .orb-box.clickable {
  cursor: pointer;
  transition: 0.18s ease;
}
.page-04-learn-electron-configuration .orb-box.clickable:hover {
  border-color: #60a5fa;
  transform: translateY(-1px);
}
.page-04-learn-electron-configuration .orb-box.orb-error {
  border-color: #fca5a5;
  background: #fef2f2;
}
.mini-workline {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  gap: 0.7rem;
  margin-top: 0.85rem;
}
.spectrum-track {
  position: relative;
  margin-top: 0.75rem;
}
.spectrum-marker {
  position: absolute;
  top: -6px;
  width: 14px;
  height: 30px;
  border-radius: 999px;
  background: rgba(15, 23, 42, 0.78);
  border: 2px solid #fff;
  box-shadow: 0 4px 12px rgba(15, 23, 42, 0.18);
  transform: translateX(-50%);
}
.spectrum-marker.predicted { background: rgba(29, 78, 216, 0.82); }
.spectrum-marker.actual { background: rgba(5, 150, 105, 0.82); top: -1px; height: 20px; }
.hydrogen-diagram {
  position: relative;
  height: 260px;
  background: linear-gradient(180deg, rgba(219, 234, 254, 0.48), rgba(255, 255, 255, 0.95));
  border: 1px solid var(--border);
  border-radius: 18px;
  overflow: hidden;
}
.hydrogen-level {
  position: absolute;
  left: 18%;
  right: 18%;
  border-top: 2px solid #94a3b8;
}
.hydrogen-level span {
  position: absolute;
  top: -0.8rem;
  left: -3.2rem;
  font-family: 'DM Mono', monospace;
  font-size: 0.84rem;
  color: var(--dim);
}
.hydrogen-arrow {
  position: absolute;
  left: 50%;
  width: 0;
  border-left: 3px solid #1d4ed8;
  transform: translateX(-50%);
}
.hydrogen-arrow::after {
  content: "";
  position: absolute;
  left: -8px;
  width: 0;
  height: 0;
  border-left: 7px solid transparent;
  border-right: 7px solid transparent;
}
.hydrogen-arrow.down::after {
  bottom: -1px;
  border-top: 11px solid #1d4ed8;
}
.hydrogen-arrow.up::after {
  top: -1px;
  border-bottom: 11px solid #1d4ed8;
}
.compare-pill {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  margin-top: 0.55rem;
  padding: 0.42rem 0.7rem;
  border-radius: 999px;
  background: var(--dark-6);
  color: var(--dim);
  font-size: 0.86rem;
}
.challenge-step-copy {
  margin-top: 0.35rem;
  font-size: 0.84rem;
  color: var(--muted);
}

/* ── 05_Learn_Periodic_Table_and_Trends.html ── */
/* Trend arrow SVG helper */
.trend-table-wrap { overflow-x: auto; margin-top: 1rem; }
.trend-note { font-size: 0.88rem; color: var(--muted); margin-top: 0.5rem; font-style: italic; }
.trend-summary {
  margin-top: 1rem;
  border: 1px solid #dbe4ee;
  border-radius: 14px;
  background: linear-gradient(180deg, #f8fbff 0%, #eef8f4 100%);
  padding: 1rem;
}
.trend-summary-title {
  font-size: 0.85rem;
  font-weight: 800;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--muted);
  margin-bottom: 0.75rem;
}
.trend-summary-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  gap: 0.75rem;
}
.trend-summary-card {
  background: var(--white-90);
  border: 1px solid #dbe4ee;
  border-radius: 12px;
  padding: 0.85rem 0.95rem;
}
.trend-summary-card h3 {
  font-size: 1rem;
  margin: 0 0 0.45rem;
}
.trend-summary-card p {
  margin: 0.35rem 0;
  font-size: 0.92rem;
  color: var(--dim);
}
.trend-summary-card strong {
  color: var(--text);
}

/* Periodic table mini-grid for the tool */
.pt-tool-grid {
  display: grid;
  grid-template-columns: repeat(18, 28px);
  gap: 2px;
  margin-top: 0.5rem;
  font-size: 0.62rem;
  overflow-x: auto;
  max-width: 100%;
  padding-bottom: 0.35rem;
}
.pt-cell {
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: 3px;
  padding: 0;
  text-align: center;
  cursor: pointer;
  transition: 0.15s ease;
  line-height: 1;
  height: 26px;
  display: flex;
  align-items: center;
  justify-content: center;
}
.pt-cell:hover { filter: brightness(0.93); border-color: rgba(15, 138, 122, 0.5); }
.page-05-learn-periodic-table-and-trends .pt-cell.selected { outline: 2px solid var(--accent); outline-offset: -2px; filter: brightness(0.9); }
.page-05-learn-periodic-table-and-trends .pt-cell .sym { font-weight: 700; font-size: 0.62rem; }
.pt-cell.empty { background: transparent; border: none; cursor: default; }
.pt-cell.metal-alkali   { background: #fee2e2; color: #7f1d1d; border-color: #fca5a5; }
.pt-cell.metal-alkaline { background: #ffedd5; color: #7c2d12; border-color: #fdba74; }
.pt-cell.metal-trans    { background: #fef3c7; color: #78350f; border-color: #fcd34d; }
.pt-cell.post-transition { background: #ede9fe; color: #4c1d95; border-color: #c4b5fd; }
.pt-cell.metalloid      { background: #d1fae5; color: #065f46; border-color: #6ee7b7; }
.pt-cell.nonmetal       { background: #dbeafe; color: #1d4ed8; border-color: #93c5fd; }
.pt-cell.halogen        { background: #e0e7ff; color: #3730a3; border-color: #a5b4fc; }
.pt-cell.noble          { background: #fae8ff; color: #701a75; border-color: #e879f9; }
.pt-cell.lanthanide     { background: #fce7f3; color: #831843; border-color: #f9a8d4; }
.pt-cell.actinide       { background: #fff1f2; color: #881337; border-color: #fda4af; }
.page-05-learn-periodic-table-and-trends .pt-info-panel {
  margin-top: 1rem;
  padding: 1rem 1.1rem;
  background: #f3fbf7;
  border: 1px solid #bee5db;
  border-radius: var(--radius-sm);
  min-height: 80px;
  display: none;
}
.page-05-learn-periodic-table-and-trends .pt-info-panel.visible { display: block; }
.page-05-learn-periodic-table-and-trends .pt-info-name { font-size: 1.1rem; font-weight: 700; color: var(--text); }
.page-05-learn-periodic-table-and-trends .pt-info-meta { font-size: 0.85rem; color: var(--dim); margin-top: 0.25rem; }
.pt-legend { display: flex; flex-wrap: wrap; gap: 0.5rem; margin-top: 1rem; }
.pt-legend-item { display: flex; align-items: center; gap: 0.4rem; font-size: 0.78rem; color: var(--dim); }
.pt-legend-dot { width: 12px; height: 12px; border-radius: 3px; flex-shrink: 0; border: 1px solid; }
.pt-legend-dot.alkali        { background: #fee2e2; border-color: #fca5a5; }
.pt-legend-dot.alkaline      { background: #ffedd5; border-color: #fdba74; }
.pt-legend-dot.transition    { background: #fef3c7; border-color: #fcd34d; }
.pt-legend-dot.post-transition { background: #ede9fe; border-color: #c4b5fd; }
.pt-legend-dot.metalloid     { background: #d1fae5; border-color: #6ee7b7; }
.pt-legend-dot.nonmetal      { background: #dbeafe; border-color: #93c5fd; }
.pt-legend-dot.halogen       { background: #e0e7ff; border-color: #a5b4fc; }
.pt-legend-dot.noble         { background: #fae8ff; border-color: #e879f9; }
.pt-legend-dot.lanthanide    { background: #fce7f3; border-color: #f9a8d4; }
.pt-legend-dot.actinide      { background: #fff1f2; border-color: #fda4af; }

.page-05-learn-periodic-table-and-trends .tool-card { display: flex; flex-direction: column; gap: 1rem; }
.tool-card-prompt {
  padding: 0.9rem 1rem;
  background: #f8fafc;
  border: 1px solid #dbe4ee;
  border-radius: 12px;
}
.tool-card-prompt-title {
  font-size: 0.75rem;
  font-weight: 800;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--muted);
  margin-bottom: 0.35rem;
}
.tool-card-prompt-text {
  font-size: 1rem;
  font-weight: 700;
  color: var(--text);
}
.tool-compare-pair {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  background: #eff6ff;
  color: #1d4ed8;
  border: 1px solid #bfdbfe;
  border-radius: 999px;
  font-size: 0.84rem;
  font-weight: 700;
  padding: 0.3rem 0.7rem;
}
.tool-value-toggle {
  margin-top: 0.8rem;
}
.tool-values {
  display: none;
  margin-top: 0.8rem;
  font-size: 0.95rem;
  color: var(--text);
}
.tool-values.visible { display: block; }
.tool-property-chip {
  display: inline-flex;
  align-items: center;
  padding: 0.28rem 0.65rem;
  border-radius: 999px;
  background: #eff6ff;
  border: 1px solid #bfdbfe;
  color: #1d4ed8;
  font-size: 0.78rem;
  font-weight: 800;
  letter-spacing: 0.04em;
  text-transform: uppercase;
}
.pt-cell.is-target {
  outline: 3px solid #0f8a7a;
  outline-offset: -2px;
  box-shadow: 0 0 0 2px rgba(15, 138, 122, 0.12);
}
.pt-cell.is-compare {
  outline: 2px solid #2563eb;
  outline-offset: -2px;
  box-shadow: 0 0 0 2px rgba(37, 99, 235, 0.10);
}
.pt-tool-instruction {
  font-size: 0.88rem;
  color: var(--dim);
}

/* ── Static PT diagrams (5.1 groups/periods, 5.2 families) ── */
.pt-diag-outer { overflow-x: auto; margin: 1.25rem 0 0.5rem; }
.pt-diag-wrap  { width: max-content; }
.pt-diag-hdr   { display: flex; align-items: center; height: 18px; margin-bottom: 2px; }
.pt-diag-hdr-lbl  { width: 20px; flex-shrink: 0; }
.pt-diag-hdr-grps { display: flex; gap: 2px; }
.pt-diag-grp-num  { width: 30px; height: 18px; display: flex; align-items: center; justify-content: center; font-size: 0.55rem; color: var(--muted); font-weight: 700; }
.pt-diag-main     { display: flex; flex-direction: column; gap: 2px; }
.pt-diag-row      { display: flex; align-items: center; gap: 2px; }
.pt-diag-period-lbl { width: 20px; flex-shrink: 0; font-size: 0.6rem; font-weight: 700; color: var(--muted); text-align: right; padding-right: 3px; }
.pt-dc { width: 30px; height: 26px; border-radius: 3px; display: flex; align-items: center; justify-content: center; font-weight: 700; font-size: 0.62rem; -webkit-user-select: none; user-select: none; flex-shrink: 0; }
.pt-dc.empty    { background: transparent; }
.pt-dc.s-blk    { background: #dbeafe; color: #1d4ed8; border: 1px solid #93c5fd; }
.pt-dc.p-blk    { background: #d1fae5; color: #065f46; border: 1px solid #6ee7b7; }
.pt-dc.d-blk    { background: #fef3c7; color: #78350f; border: 1px solid #fcd34d; }
.pt-dc.f-blk    { background: #fce7f3; color: #831843; border: 1px solid #f9a8d4; }
.pt-dc.fblk-ph  { font-size: 0.48rem; }
.pt-dc.fam-alkali   { background: #fee2e2; color: #7f1d1d; border: 1px solid #fca5a5; }
.pt-dc.fam-alkaline { background: #ffedd5; color: #7c2d12; border: 1px solid #fdba74; }
.pt-dc.fam-trans    { background: #fef3c7; color: #78350f; border: 1px solid #fcd34d; }
.pt-dc.fam-ptrans   { background: #ede9fe; color: #4c1d95; border: 1px solid #c4b5fd; }
.pt-dc.fam-metalloid{ background: #d1fae5; color: #065f46; border: 1px solid #6ee7b7; }
.pt-dc.fam-nonmetal { background: #dbeafe; color: #1d4ed8; border: 1px solid #93c5fd; }
.pt-dc.fam-halogen  { background: #e0e7ff; color: #3730a3; border: 1px solid #a5b4fc; }
.pt-dc.fam-noble    { background: #fae8ff; color: #701a75; border: 1px solid #e879f9; }
.pt-dc.fam-lant     { background: #fce7f3; color: #831843; border: 1px solid #f9a8d4; }
.pt-dc.fam-act      { background: #fff1f2; color: #881337; border: 1px solid #fda4af; }
.pt-diag-f-section  { display: flex; gap: 2px; margin-top: 6px; }
.pt-diag-f-offset   { width: 94px; flex-shrink: 0; }
.pt-diag-f-main     { display: flex; flex-direction: column; gap: 2px; }
.pt-diag-f-row      { display: flex; align-items: center; gap: 2px; }
.pt-diag-f-lbl      { width: 20px; flex-shrink: 0; font-size: 0.58rem; color: var(--muted); font-weight: 700; text-align: right; padding-right: 3px; }
.pt-diag-f-cells    { display: flex; gap: 2px; }
.pt-diag-arrows { display: flex; flex-wrap: wrap; gap: 0.75rem; margin-top: 0.9rem; font-size: 0.8rem; color: var(--dim); }
.pt-diag-arrow-badge { display: inline-flex; align-items: center; font-weight: 700; padding: 0.18rem 0.5rem; border-radius: 999px; font-size: 0.76rem; margin-right: 0.3rem; }
.arrow-period { background: #dbeafe; color: #1d4ed8; }
.arrow-group  { background: #d1fae5; color: #065f46; }
.fam-legend { display: flex; flex-wrap: wrap; gap: 0.5rem; margin-top: 1rem; }
.fam-legend-item { display: flex; align-items: center; gap: 0.35rem; font-size: 0.78rem; color: var(--dim); }
.fam-dot { width: 12px; height: 12px; border-radius: 3px; flex-shrink: 0; }
/* org-mode axis label layout */
.pt-diag-outer-flex { display: flex; gap: 0.75rem; align-items: flex-start; width: max-content; }
.pt-diag-y-axis {
  align-self: stretch;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  width: 82px;
  min-width: 82px;
  font-size: 0.7rem;
  color: var(--dim);
  text-align: center;
  line-height: 1.55;
  padding: 0.5rem 0.35rem;
  gap: 0.45rem;
  border-right: 2px solid #bfdbfe;
}
.pt-diag-y-axis .axis-badge {
  display: inline-block;
  background: #dbeafe;
  color: #1d4ed8;
  font-weight: 700;
  padding: 0.15rem 0.45rem;
  border-radius: 999px;
  font-size: 0.71rem;
  white-space: nowrap;
}
/* fam-mode: table + legend side by side */
.pt-diag-fam-outer { display: flex; align-items: flex-start; width: max-content; }
.fam-legend-side {
  display: flex;
  flex-direction: column;
  gap: 0.35rem;
  padding-left: 1.1rem;
  margin-left: 0.6rem;
  border-left: 2px solid var(--border);
  align-self: flex-start;
  margin-top: 1.5rem;
}

/* ── 06_Learn_Chemistry_Nomenclature.html ── */
/* Nomenclature tool styles */
.naming-tool-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1rem;
  margin-top: 1rem;
}

.tool-section-label {
  font-size: 0.78rem;
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--accent2);
  margin: 1rem 0 0.5rem;
}

.page-06-learn-chemistry-nomenclature .tool-result-box {
  background: #eff6ff;
  border: 1px solid #bfdbfe;
  border-radius: var(--radius-sm);
  padding: 0.9rem 1rem;
  font-size: 1.05rem;
  font-weight: 600;
  color: #1e3a8a;
  min-height: 2.8rem;
  display: block;
  line-height: 1.55;
  font-family: inherit;
}

.page-06-learn-chemistry-nomenclature .tool-result-box.error {
  background: #fef2f2;
  border-color: #fecaca;
  color: #991b1b;
}

.page-06-learn-chemistry-nomenclature select.prob-input {
  appearance: none;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='13' height='8'%3E%3Cpath d='M0 0l6 8 6-8z' fill='%2364748b'/%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: right 0.75rem center;
  padding-right: 2rem;
}

/* Hi-Lo scaffolding aids */
.scaffold-box {
  background: #f0fdf4;
  border: 1px solid #86efac;
  border-radius: var(--radius-sm);
  padding: 0.85rem 1rem;
  margin-top: 0.85rem;
  font-size: 0.94rem;
}
.scaffold-box .scaffold-label {
  font-size: 0.74rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: #059669;
  margin-bottom: 0.3rem;
}

.ion-table th { background: #eff6ff; }
.ion-table td:first-child { font-family: 'DM Mono', monospace; font-weight: 600; color: var(--accent2); }
.polyatomic-ion-table {
  display: block;
  overflow: visible;
}
.polyatomic-ion-table caption {
  position: absolute;
  width: 1px;
  height: 1px;
  overflow: hidden;
  clip: rect(0 0 0 0);
  clip-path: inset(50%);
  white-space: nowrap;
}
.polyatomic-ion-table thead {
  position: absolute;
  width: 1px;
  height: 1px;
  overflow: hidden;
  clip: rect(0 0 0 0);
  clip-path: inset(50%);
  white-space: nowrap;
}
.polyatomic-ion-table tbody {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(min(100%, 21rem), 1fr));
  gap: 0.55rem 0.8rem;
}
.polyatomic-ion-table tr {
  display: grid;
  grid-template-columns: minmax(5.5rem, 0.85fr) minmax(8rem, 1.25fr) minmax(4rem, 0.55fr);
  align-items: stretch;
  overflow: hidden;
  border: 1px solid rgba(217, 200, 180, 0.82);
  border-radius: 10px;
  background: var(--white-82);
}
.polyatomic-ion-table td {
  display: flex;
  align-items: center;
  border-bottom: 0;
  border-right: 1px solid rgba(217, 200, 180, 0.72);
  padding: 0.62rem 0.75rem;
}
.polyatomic-ion-table td:last-child {
  border-right: 0;
  justify-content: center;
  font-weight: 700;
  color: var(--accent2);
}
@media (max-width: 520px) {
  .polyatomic-ion-table tr {
    grid-template-columns: minmax(4.9rem, 0.8fr) minmax(7rem, 1.3fr) minmax(3.4rem, 0.55fr);
  }

  .polyatomic-ion-table td {
    padding: 0.56rem 0.58rem;
    font-size: 0.88rem;
  }
}

.mt-075 { margin-top: 0.75rem; }
.mt-1 { margin-top: 1rem; }
.comp-type-select { margin-bottom: 0.75rem; }
.page-06-learn-chemistry-nomenclature .tool-hint { font-size: 0.88rem; color: var(--muted); }
.roman-input-row {
  display: flex;
  gap: 0.75rem;
  flex-wrap: wrap;
  margin-top: 0.5rem;
}
.roman-input {
  flex: 1;
}
.roman-input.w-140 { min-width: 140px; }
.roman-input.w-100 { min-width: 100px; }
.roman-input.w-160 { min-width: 160px; }
.roman-btn,
.roman-result { margin-top: 0.75rem; }
.roman-result {
  font-family: 'DM Mono', monospace;
}
.quiz-formula {
  margin-top: 0.35rem;
  font-size: 1.7rem;
  font-weight: 700;
  color: var(--ink);
  letter-spacing: 0.01em;
  font-family: 'DM Mono', monospace;
}
.quiz-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  margin-top: 1rem;
}
.page-06-learn-chemistry-nomenclature .tool-result-box.success {
  background: #ecfdf5;
  border-color: #86efac;
  color: #166534;
}
.page-06-learn-chemistry-nomenclature .tool-reveal h3 {
  margin: 0 0 0.55rem;
  font-size: 1rem;
}
.page-06-learn-chemistry-nomenclature .tool-reveal ul {
  margin: 0;
  padding-left: 1.2rem;
}
.page-06-learn-chemistry-nomenclature .tool-reveal p + p,
.page-06-learn-chemistry-nomenclature .tool-reveal p + ul,
.page-06-learn-chemistry-nomenclature .tool-reveal ul + p {
  margin-top: 0.55rem;
}
.page-06-learn-chemistry-nomenclature .tool-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  margin-top: 1rem;
}
.page-06-learn-chemistry-nomenclature .tool-actions .btn[disabled] {
  opacity: 0.55;
  cursor: not-allowed;
}

/* ── 07_Learn_Chemistry_Moles.html ── */
.mole-spotlight {
  background: linear-gradient(180deg, rgba(255,255,255,0.98), rgba(246,248,255,0.96));
}
.molar-mass-table-mobile th,
.molar-mass-table-mobile td {
  font-size: 0.95rem;
}
.mole-figure {
  margin: 1rem 0 0;
  padding: 1rem;
  border: 1px solid rgba(191, 219, 254, 0.9);
  border-radius: var(--radius-sm);
  background: #fff;
}
.mole-figure img {
  display: block;
  width: 100%;
  height: auto;
}
.mole-figure figcaption {
  margin-top: 0.8rem;
  font-size: 0.92rem;
  color: var(--muted);
}
.particle-model-figure {
  margin: 1rem 0 0;
  padding: 1rem;
  border: 1px solid rgba(191, 219, 254, 0.9);
  border-radius: var(--radius-sm);
  background: #fff;
}
.particle-model-crop {
  overflow: hidden;
  aspect-ratio: 1678 / 315;
  border-radius: calc(var(--radius-sm) - 4px);
  background: linear-gradient(180deg, #f8fbff, #eef4ff);
}
.particle-model-crop img {
  display: block;
  width: 100%;
  height: auto;
  transform: translateY(-0.5%);
}
.particle-summary-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.85rem;
  margin-top: 1rem;
}
.particle-wrapper {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 1rem;
  margin-top: 1rem;
}
.particle-summary-box {
  background: #f8fafc;
  border: 1px solid #dbeafe;
  border-radius: var(--radius-sm);
  padding: 0.95rem 1rem;
  min-width: 0;
  text-align: center;
  line-height: 1.6;
  box-shadow: 0 2px 5px rgba(15, 23, 42, 0.05);
}
.particle-summary-box strong {
  display: block;
  color: var(--accent2);
  margin-bottom: 0.35rem;
}
.particle-summary-box svg {
  display: block;
  width: auto;
  height: 80px;
  margin: 0 auto 0.9rem;
}
.nowrap {
  white-space: nowrap;
}
.mole-summary-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.85rem;
  margin-top: 1rem;
}
.mole-summary-box {
  background: #f8fafc;
  border: 1px solid #dbeafe;
  border-radius: var(--radius-sm);
  padding: 0.9rem 1rem;
}
.mole-summary-box strong {
  display: block;
  color: var(--accent2);
  margin-bottom: 0.35rem;
}
.page-07-learn-chemistry-moles .tool-choice-btn.reveal-correct,
.page-07-learn-chemistry-moles .explore-choice.reveal-correct {
  border-color: #86efac;
  background: #ecfdf5;
  color: #166534;
}
.reaction-band {
  margin-top: 1rem;
  padding: 0.9rem 1rem;
  border-radius: var(--radius-sm);
  background: #eff6ff;
  border: 1px solid #bfdbfe;
  font-family: 'DM Mono', monospace;
  font-size: 1.05rem;
  text-align: center;
  color: #1e3a8a;
}
.setup-preview-note {
  margin-top: 0.75rem;
  color: var(--muted);
  font-size: 0.92rem;
  line-height: 1.5;
}
.setup-preview-box {
  margin-top: 1rem;
}
.page-07-learn-chemistry-moles .setup-preview-box .fl-chain {
  margin-top: 0.5rem;
}
.setup-preview-top,
.setup-preview-bottom {
  min-width: 12ch;
  display: inline-block;
}
.setup-roadmap {
  margin-top: 1rem;
  padding: 0.95rem 1rem;
  border-radius: var(--radius-sm);
  background: #f8fafc;
  border: 1px solid #dbeafe;
}
.setup-roadmap strong {
  color: var(--accent2);
}
.setup-coach-stage {
  grid-template-columns: 1fr;
}
.setup-coach-media-grid {
  display: grid;
  gap: 0.85rem;
}
.setup-coach-media-support {
  display: grid;
  grid-template-columns: minmax(180px, 0.85fr) minmax(240px, 1.15fr);
  gap: 0.85rem;
  align-items: start;
}
.setup-coach-panel {
  padding: 1.15rem;
}
.tool-support-panel {
  margin-top: 0.85rem;
  padding: 0.9rem 1rem;
  border-radius: var(--radius-sm);
  background: #f8fafc;
  border: 1px solid #dbeafe;
}
.tool-support-panel strong {
  color: var(--accent2);
}
.tool-checker-note {
  margin-top: 0.75rem;
  font-size: 0.92rem;
  color: var(--muted);
}
.coach-solved-work {
  display: grid;
  gap: 0.7rem;
}
.coach-solved-chainline,
.coach-solved-answerline {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.55rem;
  line-height: 1.7;
}
.page-07-learn-chemistry-moles .coach-solved-chainline .fl-frac {
  min-width: 148px;
}
.coach-solved-answerline {
  padding-top: 0.2rem;
  border-top: 1px dashed rgba(15, 110, 86, 0.2);
  color: var(--text);
  font-size: 1.02rem;
}
.page-07-learn-chemistry-moles .coach-solved-answerline .equals-mark {
  font-weight: 700;
  color: var(--accent2);
}
.mole-wheel-shell {
  margin-top: 1rem;
}
.mole-wheel-stack {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0;
}
.mole-wheel-svg {
  width: 100%;
  max-width: 340px;
  overflow: visible;
}
.mole-wheel-node {
  cursor: pointer;
}
.mole-wheel-panel {
  width: 100%;
  max-width: 500px;
  min-height: 120px;
  margin-top: 0.5rem;
  padding: 1rem;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: var(--surface);
}
.mole-wheel-title {
  margin-bottom: 0.5rem;
  font-size: 0.85rem;
  font-weight: 500;
  color: var(--muted);
}
.mole-wheel-body {
  font-size: 0.82rem;
  line-height: 1.5;
  color: var(--dim);
}
.conv-group-full {
  grid-column: 1 / -1;
}
.conv-result-tall {
  min-height: 3rem;
}
.mole-wheel-direction {
  margin-right: 4px;
  padding: 3px 9px;
  border: 1px solid var(--border);
  border-radius: 20px;
  background: transparent;
  color: var(--muted);
  font-size: 0.75rem;
  cursor: pointer;
}
.mole-wheel-rule {
  margin-bottom: 6px;
  font-size: 0.82rem;
  font-weight: 500;
  color: var(--text);
}
.mole-wheel-note {
  margin-bottom: 6px;
  font-size: 0.78rem;
  color: var(--dim);
}
.composition-result-start {
  color: var(--text);
}
.composition-result-molar-mass {
  color: var(--gold);
}
.composition-result-element {
  color: var(--accent2);
}
.composition-result-percent {
  color: var(--green);
}
.example-roadmap {
  margin-top: 0.85rem;
  padding: 0.9rem 1rem;
  border: 1px solid #dbeafe;
  border-radius: var(--radius-sm);
  background: #f8fbff;
}
.example-roadmap-title {
  margin: 0 0 0.45rem;
  font-size: 0.78rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--accent2);
}
.example-roadmap-steps {
  display: flex;
  flex-wrap: wrap;
  gap: 0.45rem;
  align-items: center;
  color: var(--text);
}
.example-roadmap-step {
  padding: 0.38rem 0.6rem;
  border-radius: 999px;
  background: #fff;
  border: 1px solid rgba(147, 197, 253, 0.7);
  font-size: 0.92rem;
  line-height: 1.4;
}
.example-roadmap-arrow {
  color: var(--muted);
  font-weight: 700;
}
@media (max-width: 720px) {
  .molar-mass-table-mobile th,
  .molar-mass-table-mobile td {
    font-size: 0.82rem;
    padding: 0.58rem 0.55rem;
  }
}
@media (max-width: 760px) {
  .particle-summary-grid,
  .particle-wrapper,
  .mole-summary-grid {
    grid-template-columns: 1fr;
  }
  .setup-coach-media-support {
    grid-template-columns: 1fr;
  }
}

/* ── 08_Learn_Chemical_Reactions.html ── */
/* ── Reaction type badge colors ── */
.rxn-badge {
  display: inline-block;
  font-size: 0.78rem;
  font-weight: 650;
  letter-spacing: 0.07em;
  text-transform: uppercase;
  padding: 0.22rem 0.6rem;
  border-radius: 999px;
  margin-right: 0.35rem;
}
.badge-precip  { background: #fef3c7; color: #92400e; }
.badge-acid    { background: #ecfdf5; color: #065f46; }
.badge-redox   { background: #ede9fe; color: #5b21b6; }
.badge-synth   { background: #dbeafe; color: #1e40af; }
.badge-decomp  { background: #fee2e2; color: #991b1b; }
.badge-single  { background: #fce7f3; color: #9d174d; }
.badge-double  { background: #e0f2fe; color: #075985; }
.badge-combustion { background: #ffedd5; color: #9a3412; }

/* ── Oxidation number inline display ── */
.ox-table {
  display: flex;
  flex-wrap: wrap;
  gap: 0.55rem;
  margin-top: 0.85rem;
}
.ox-chip {
  display: flex;
  flex-direction: column;
  align-items: center;
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 0.5rem 0.9rem;
  min-width: 64px;
}
.ox-chip .ox-formula { font-family: 'DM Mono', monospace; font-size: 0.92rem; font-weight: 500; color: var(--text); }
.ox-chip .ox-num { font-size: 0.78rem; font-weight: 700; color: var(--accent2); margin-top: 0.15rem; }

/* ── Equation display ── */
.eq-display {
  font-family: 'DM Mono', monospace;
  font-size: 1.05rem;
  background: #eff6ff;
  border: 1px solid #bfdbfe;
  border-radius: var(--radius-sm);
  padding: 0.85rem 1rem;
  color: #1e3a8a;
  margin: 0.75rem 0;
  overflow-x: auto;
  white-space: nowrap;
}
.eq-coeff { color: var(--accent2); font-weight: 700; }
.eq-arrow { color: var(--muted); margin: 0 0.4rem; }
.eq-state { font-size: 0.82rem; color: var(--muted); }

.tool-subhead {
  font-size: 0.82rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--muted);
  margin-bottom: 0.35rem;
}
.tool-steps {
  margin: 0.55rem 0 0;
  padding-left: 1.1rem;
}
.tool-steps li {
  margin: 0.35rem 0;
}

/* ── Net ionic step layout ── */
.ionic-step {
  display: flex;
  gap: 0.75rem;
  align-items: flex-start;
  padding: 0.6rem 0;
  border-bottom: 1px dashed var(--border);
}
.ionic-step:last-child { border-bottom: none; }
.ionic-label {
  font-size: 0.75rem;
  font-weight: 650;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--accent2);
  min-width: 80px;
  padding-top: 0.15rem;
  flex-shrink: 0;
}

/* ── 09_Learn_Chemistry_Stoichiometry.html ── */
/* ── Hi-Lo specific helpers (no new classes, just semantic tweaks) ── */
.vocab-row {
  display: grid;
  grid-template-columns: auto 1fr;
  gap: 0.5rem 1rem;
  align-items: baseline;
  margin-top: 0.75rem;
}
.vocab-term {
  font-weight: 700;
  color: var(--accent2);
  white-space: nowrap;
}
.road-map {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  align-items: center;
  margin: 0.9rem 0 0.4rem;
  font-size: 0.92rem;
}
.road-step {
  background: #dbeafe;
  color: #1e40af;
  border-radius: 999px;
  padding: 0.3rem 0.8rem;
  font-weight: 600;
  white-space: nowrap;
}
.road-arrow {
  color: var(--muted);
  font-size: 1.1rem;
}
.highlight-box {
  background: #fef9c3;
  border: 1px solid #fde047;
  border-radius: var(--radius-sm);
  padding: 0.85rem 1rem;
  margin-top: 0.9rem;
  color: #713f12;
  font-size: 0.95rem;
}
.highlight-box strong { color: #92400e; }
.mini-visual-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.8rem;
  margin-top: 0.95rem;
}
.mini-visual-card {
  padding: 0.9rem 0.95rem;
  border: 1px solid #bfdbfe;
  border-radius: var(--radius-sm);
  background: linear-gradient(180deg, #ffffff, #eff6ff);
}
.mini-visual-card .mini-label {
  display: block;
  margin-bottom: 0.35rem;
  color: var(--accent2);
  font-size: 0.76rem;
  font-weight: 800;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}
.mini-visual-card .mini-value {
  font-family: 'DM Mono', monospace;
  color: #1e3a8a;
  font-size: 1.02rem;
}
.mini-visual-card .mini-copy {
  margin: 0.45rem 0 0;
  font-size: 0.9rem;
  line-height: 1.5;
  color: var(--ink);
}
.compare-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.8rem;
  margin-top: 0.95rem;
}
.compare-card {
  padding: 0.9rem 0.95rem;
  border: 1px solid #d9c8b4;
  border-radius: var(--radius-sm);
  background: linear-gradient(180deg, #ffffff, #fff8ed);
}
.compare-card strong {
  color: var(--accent2);
}
.compare-card p {
  margin: 0.35rem 0 0;
  line-height: 1.5;
}
.check-list {
  list-style: none;
  padding: 0;
  margin: 0.75rem 0 0;
}
.check-list li {
  padding: 0.35rem 0 0.35rem 1.6rem;
  position: relative;
  font-size: 0.95rem;
  border-bottom: 1px dashed var(--border);
}
.check-list li:last-child { border-bottom: none; }
.check-list li::before {
  content: '✓';
  position: absolute;
  left: 0;
  color: var(--green);
  font-weight: 700;
}

/* ── Tool UI ── */
.ratio-choice-fraction {
  display: inline-grid;
  justify-items: center;
  gap: 0.2rem;
  min-width: 120px;
}
.ratio-choice-frac-line {
  width: 100%;
  max-width: 180px;
  height: 2px;
  background: currentColor;
}
.ratio-choice-prefix,
.ratio-choice-suffix {
  font-family: inherit;
  font-size: 0.95rem;
}
.ratio-choice-num,
.ratio-choice-den {
  font-family: inherit;
  text-align: center;
  line-height: 1.3;
}
.inline-frac {
  display: inline-grid;
  justify-items: center;
  vertical-align: middle;
  margin: 0 0.15rem;
  min-width: 90px;
}
.inline-frac-num,
.inline-frac-den {
  font-family: 'DM Mono', monospace;
  color: #1e3a8a;
  text-align: center;
  line-height: 1.25;
}
.inline-frac-bar {
  width: 100%;
  height: 2px;
  background: #1e3a8a;
  margin: 0.12rem 0;
}

.page-01-learn-intro-to-chemistry-and-lab-safety .unit01-balance-svg {
  max-width: 320px;
  display: block;
  margin: 0 auto;
}

.page-02-learn-chemistry-matter .u02-svg-block {
  display: block;
}

.page-02-learn-chemistry-matter .u02-mt-12 {
  margin-top: 12px;
}

.page-02-learn-chemistry-matter .u02-mt-8 {
  margin-top: 8px;
}

.page-02-learn-chemistry-matter .u02-my-10 {
  margin: 10px 0;
}

.page-02-learn-chemistry-matter .u02-note-caption {
  margin-top: 6px;
  font-size: 0.85em;
  color: #475569;
}

.page-03-learn-atomic-structure .tool1-prompt-min {
  min-height: 5.25rem;
}

.page-03-learn-atomic-structure .tool2-scenario-control {
  margin-top: 0.85rem;
  max-width: 360px;
}

.page-03-learn-atomic-structure .tool2-prompt-min {
  min-height: 4rem;
}

.page-03-learn-atomic-structure .tool3-formula-select {
  max-width: 340px;
  margin-top: 0.5rem;
}

.page-09-learn-chemistry-stoichiometry .sto-mt-08 {
  margin-top: 0.8rem;
}

.page-09-learn-chemistry-stoichiometry .sto-mt-075 {
  margin-top: 0.75rem;
}

.page-09-learn-chemistry-stoichiometry .sto-mt-085 {
  margin-top: 0.85rem;
}

.page-09-learn-chemistry-stoichiometry .sto-mt-07 {
  margin-top: 0.7rem;
}

.page-14-learn-chemistry-equilibrium #beam-group {
  transform-origin: 320px 248px;
  transition: transform 0.8s cubic-bezier(0.34, 1.56, 0.64, 1);
}

.page-14-learn-chemistry-equilibrium #shift-arrow {
  transition: opacity 0.4s;
}

.strategy-guides-label {
  margin-bottom: 0.85rem;
}

.round-label {
  font-size: 0.88rem;
  color: var(--muted);
  margin: 0 0 0.75rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.08em;
}

.round-label.round-label-gap {
  margin: 1rem 0 0.75rem;
}

/* ── 10_Learn_Chemistry_Bonding.html ── */
.page-10-learn-chemistry-bonding {
  --vsepr-b-fill: #eff6ff;
  --vsepr-b-stroke: #3b82f6;
  --vsepr-b-text: #2563eb;
  --vsepr-a-fill: #fef2f2;
  --vsepr-a-stroke: #ef4444;
  --vsepr-a-text: #dc2626;
  --vsepr-bond-color: #334155;
  --vsepr-lp-stroke: #94a3b8;
}

.bond {
  stroke: var(--vsepr-bond-color);
  stroke-width: 2.5;
  stroke-linecap: round;
}

.bond-dash {
  stroke: var(--vsepr-bond-color);
  stroke-width: 2.5;
  stroke-linecap: round;
  stroke-dasharray: 4, 4;
}

.wedge {
  fill: var(--vsepr-bond-color);
}

.atom-b {
  fill: var(--vsepr-b-fill);
  stroke: var(--vsepr-b-stroke);
  stroke-width: 2;
}

.atom-a {
  fill: var(--vsepr-a-fill);
  stroke: var(--vsepr-a-stroke);
  stroke-width: 2;
}

.text-b {
  fill: var(--vsepr-b-text);
  font-weight: 800;
  font-size: 14px;
  font-family: sans-serif;
  text-anchor: middle;
  dominant-baseline: central;
}

.text-a {
  fill: var(--vsepr-a-text);
  font-weight: 800;
  font-size: 12px;
  font-family: sans-serif;
  text-anchor: middle;
  dominant-baseline: central;
}

.lp {
  fill: #ffffff;
  stroke: var(--vsepr-lp-stroke);
  stroke-width: 1.5;
  stroke-dasharray: 3, 3;
}

.text-lp {
  fill: var(--vsepr-lp-stroke);
  font-weight: 700;
  font-size: 9px;
  font-family: sans-serif;
  text-anchor: middle;
  dominant-baseline: central;
}
/* ── Unit 10: all-screen SVG baseline ──────────────────────────────── */

/* Every SVG on this page scales down gracefully and never overflows */
.page-10-learn-chemistry-bonding svg {
  max-width: 100%;
  height: auto;
}

.vsepr-example-card {
  max-width: 360px;
  margin: 1rem auto 0;
}

/* Resonance structure SVGs: intrinsic pixel size on desktop, centred */
.resonance-structure svg {
  display: block;
  max-width: 100%;
  height: auto;
  margin-inline: auto;
}

/* Polarity / dipole diagram SVGs: intrinsic size, centred in card */
.page-10-learn-chemistry-bonding .diagram-card svg {
  display: block;
  max-width: 100%;
  height: auto;
  margin-inline: auto;
}

.page-10-learn-chemistry-bonding .hb-water-svg {
  max-width: 460px;
}

.page-10-learn-chemistry-bonding .center-note.center-note-narrow {
  max-width: 34rem;
}

.page-13-learn-chemistry-solutions .sol-mt-075 {
  margin-top: 0.75rem;
}

.page-13-learn-chemistry-solutions .sol-mt-05 {
  margin-top: 0.5rem;
}

.page-13-learn-chemistry-solutions .conc-table.conc-table-spaced {
  margin-top: 0.8rem;
}

.page-13-learn-chemistry-solutions .particle-list {
  margin: 0.5rem 0 0.75rem 1.2rem;
  line-height: 1.9;
}

.page-13-learn-chemistry-solutions .legend-row {
  display: flex;
  flex-wrap: wrap;
  gap: 0.55rem 0.9rem;
  align-items: center;
}

.page-13-learn-chemistry-solutions .legend-title {
  color: var(--text);
  font-size: 0.8rem;
  text-transform: uppercase;
  letter-spacing: 0.07em;
  width: 100%;
  margin-bottom: 0.1rem;
}

.page-13-learn-chemistry-solutions .legend-dot {
  display: inline-block;
  width: 12px;
  height: 12px;
  border-radius: 999px;
  margin-right: 0.35rem;
  vertical-align: -1px;
}

.page-13-learn-chemistry-solutions .legend-dot.legend-na { background: #3b82f6; }
.page-13-learn-chemistry-solutions .legend-dot.legend-cl { background: #ef4444; }
.page-13-learn-chemistry-solutions .legend-dot.legend-glucose { background: #10b981; }
.page-13-learn-chemistry-solutions .legend-dot.legend-ag { background: #8b5cf6; }
.page-13-learn-chemistry-solutions .legend-dot.legend-no3 { background: #f97316; }
.page-13-learn-chemistry-solutions .legend-dot.legend-agcl {
  background: #d1d5db;
  border: 1.5px solid #6b7280;
}

.resonance-row--nitrate {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0.8rem;
  margin: 1rem 0 0.6rem;
  overflow-x: auto;
  padding: 0.25rem 0 0.5rem;
}

.resonance-structure {
  flex: 0 0 auto;
  text-align: center;
}

.resonance-structure svg {
  display: block;
}

.resonance-arrow {
  flex: 0 0 auto;
  color: #2563eb;
  font-size: 1.75rem;
  font-weight: 800;
  line-height: 1;
}

@media (max-width: 900px) {
  .resonance-row--nitrate {
    justify-content: flex-start;
  }
}

@media (max-width: 480px) {
  .page-10-learn-chemistry-bonding .lewis-diagram {
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 12px;
    margin: 18px auto;
  }

  .page-10-learn-chemistry-bonding .lewis-box {
    min-height: 0;
    max-width: none;
    padding: 12px 10px;
  }

  .page-10-learn-chemistry-bonding .lewis-box svg {
    width: min(100%, 88px);
  }

  .page-10-learn-chemistry-bonding .lb-name {
    margin-bottom: 8px;
    font-size: 0.95rem;
  }

  .page-10-learn-chemistry-bonding .lb-formula {
    margin-top: 8px;
    font-size: 0.76rem;
  }

  .page-10-learn-chemistry-bonding .vsepr-diagram-shell {
    max-width: 180px;
    margin-inline: auto;
  }

  .page-10-learn-chemistry-bonding .vsepr-diagram {
    min-height: 0;
  }

  .page-10-learn-chemistry-bonding .vsepr-diagram svg {
    width: min(100%, 170px);
    margin-inline: auto;
  }

  .page-10-learn-chemistry-bonding .geo-card svg,
  .page-10-learn-chemistry-bonding .vsepr-example-card svg {
    width: min(100%, 158px);
  }

  .page-10-learn-chemistry-bonding .diagram-card svg {
    width: min(100%, 210px);
    margin-inline: auto;
    display: block;
  }

  .page-10-learn-chemistry-bonding .resonance-structure svg {
    width: min(100%, 148px);
    height: auto;
    margin-inline: auto;
  }

  .resonance-row--nitrate {
    flex-direction: column;
    align-items: center;
    justify-content: flex-start;
    overflow-x: visible;
  }

  .resonance-arrow {
    transform: rotate(90deg);
  }
}