:root {
      --bg: #0e1c17;
      --bg2: #13271f;
      --panel: #193024;
      --panel2: #1f3a2c;
      --line: #2c4a3a;
      --line2: #3a5e49;
      --ink: #f1ecdd;
      --ink-dim: #b4c3b3;
      --ink-faint: #7f9285;
      --paper: #f6f1e4;
      --paper-ink: #222a20;
      --paper-dim: #5a6553;
      --paper-line: #ddd2ba;
      --gold: #e2b35f;
      --gold-deep: #c0922f;
      --plant: #62b173;
      --plant-d: #2f6b40;
      --animal: #e58a5d;
      --animal-d: #a8512a;
      --morph: #5fb6c4;
      --morph-d: #2c7e8c;
      --anat: #bb8ed6;
      --anat-d: #7f4ea0;
      --ok: #5fc27e;
      --bad: #e9745f;
      --warn: #e2b35f;
      --r: 16px;
      --rs: 10px;
      --sans: 'Inter', system-ui, -apple-system, sans-serif;
      --serif: 'Fraunces', 'Georgia', serif;
      --mono: 'Spline Sans Mono', ui-monospace, monospace;
      --shadow: 0 10px 30px -12px rgba(0, 0, 0, .6);
      --c: var(--gold);
      --c-d: var(--gold-deep);
    }

    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0
    }

    html {
      scroll-behavior: smooth
    }

    body {
      font-family: var(--sans);
      background: var(--bg);
      color: var(--ink);
      line-height: 1.55;
      -webkit-font-smoothing: antialiased;
      background-image: radial-gradient(1200px 600px at 80% -10%, #1b3527 0, transparent 60%),
        radial-gradient(900px 500px at -10% 110%, #16291f 0, transparent 55%);
      background-attachment: fixed;
      min-height: 100vh;
      overflow-x: hidden;
    }

    ::selection {
      background: var(--gold);
      color: #1a130a
    }

    button {
      font-family: inherit;
      cursor: pointer;
      border: none;
      background: none;
      color: inherit
    }

    .hidden {
      display: none !important
    }

    /* ---------- Top bar ---------- */
    .topbar {
      position: sticky;
      top: 0;
      z-index: 50;
      display: flex;
      align-items: center;
      gap: 14px;
      padding: 12px clamp(14px, 4vw, 40px);
      background: rgba(14, 28, 23, .82);
      backdrop-filter: blur(12px);
      border-bottom: 1px solid var(--line);
    }

    .brand {
      display: flex;
      align-items: center;
      gap: 11px;
      cursor: pointer
    }

    .brand .mark {
      width: 38px;
      height: 38px;
      border-radius: 11px;
      flex: none;
      display: grid;
      place-items: center;
      background: linear-gradient(135deg, #1f3a2c, #0e1c17);
      border: 1px solid var(--gold);
      font-size: 22px;
      box-shadow: 0 6px 18px -6px rgba(226,179,95,.35);
    }

    .brand h1 {
      font-family: var(--serif);
      font-weight: 600;
      font-size: 18px;
      letter-spacing: .2px;
      line-height: 1.05
    }

    .brand h1 span {
      display: block;
      font-family: var(--sans);
      font-weight: 600;
      font-size: 10.5px;
      letter-spacing: .16em;
      text-transform: uppercase;
      color: var(--ink-faint)
    }

    .topbar .spacer {
      flex: 1
    }

    .xp-pill {
      display: flex;
      align-items: center;
      gap: 9px;
      background: var(--panel);
      border: 1px solid var(--line);
      padding: 7px 13px;
      border-radius: 999px;
      font-size: 13px
    }

    .xp-pill b {
      font-family: var(--mono);
      color: var(--gold);
      font-weight: 600
    }

    .lvl-badge {
      font-size: 11px;
      font-weight: 700;
      color: var(--bg);
      background: var(--gold);
      padding: 2px 8px;
      border-radius: 999px
    }

    .icon-btn {
      width: 38px;
      height: 38px;
      border-radius: 10px;
      border: 1px solid var(--line);
      background: var(--panel);
      display: grid;
      place-items: center;
      font-size: 16px;
      transition: .18s
    }

    .icon-btn:hover {
      border-color: var(--gold);
      color: var(--gold)
    }

    /* === TOPBAR MOBILE === */
    @media (max-width: 600px) {
      .topbar {
        padding: 8px 12px;
        gap: 6px;
      }
      .brand .mark {
        display: none;
      }
      .brand h1 {
        font-size: 15px; /* slight bump for readability */
        letter-spacing: 0;
        white-space: nowrap; /* prevent 'The Smart Bio Notes' from wrapping to two lines */
      }
      .brand h1 span {
        display: none;
      }
      /* Collapse XP pill to just the number, no level badge text */
      .xp-pill {
        padding: 5px 9px;
        font-size: 11.5px;
        gap: 5px;
      }
      .lvl-badge {
        display: none;   /* hide on very small screens, show on ≥380px */
      }
      .icon-btn {
        width: 30px;
        height: 30px;
        font-size: 13px;
        border-radius: 8px;
      }
    }
    /* Show level badge back on slightly wider phones */
    @media (min-width: 380px) and (max-width: 600px) {
      .lvl-badge { display: inline; }
    }
    
    /* Extreme small screens (prevent horizontal overflow) */
    @media (max-width: 400px) {
      .icon-btn[title="Reset all progress"] { display: none; }
    }

    main {
      max-width: 1080px;
      margin: 0 auto;
      padding: clamp(18px, 4vw, 40px) clamp(14px, 4vw, 40px) 90px
    }

    /* ---------- Hero / Home ---------- */
    .hero {
      position: relative;
      padding: 30px 0 8px;
      text-align: center
    }

    .eyebrow {
      font-size: 11px;
      letter-spacing: .28em;
      text-transform: uppercase;
      color: var(--gold);
      font-weight: 700;
      margin-bottom: 14px
    }

    .hero h2 {
      font-family: var(--serif);
      font-weight: 900;
      font-size: clamp(34px, 7vw, 62px);
      line-height: .98;
      letter-spacing: -.02em
    }

    .hero h2 em {
      font-style: italic;
      font-weight: 500;
      color: var(--gold)
    }

    .hero p {
      max-width: 560px;
      margin: 16px auto 0;
      color: var(--ink-dim);
      font-size: 15.5px
    }

    .hero-stats {
      display: grid;
      grid-template-columns: repeat(4, 1fr);
      gap: 26px;
      justify-content: center;
      margin-top: 26px;
    }
    @media (max-width: 600px) {
      .hero-stats {
        grid-template-columns: 1fr 1fr;
        row-gap: 20px;
        column-gap: 10px;
      }
    }

    .hero-stat {
      text-align: center
    }

    .hero-stat b {
      display: block;
      font-family: var(--mono);
      font-size: 24px;
      color: var(--ink)
    }

    .hero-stat span {
      font-size: 11px;
      letter-spacing: .12em;
      text-transform: uppercase;
      color: var(--ink-faint)
    }

    .section-label {
      display: flex;
      align-items: center;
      gap: 14px;
      margin: 42px 0 18px
    }

    .section-label h3 {
      font-family: var(--serif);
      font-size: 22px;
      font-weight: 600;
      white-space: nowrap
    }

    .section-label .rule {
      height: 1px;
      background: linear-gradient(90deg, var(--line2), transparent);
      flex: 1
    }

    .section-label .n {
      font-family: var(--mono);
      font-size: 12px;
      color: var(--ink-faint);
      border: 1px solid var(--line);
      border-radius: 6px;
      padding: 2px 7px
    }

    /* ---------- Chapter cards ---------- */
    .chapters {
      display: grid;
      grid-template-columns: repeat(auto-fit, minmax(230px, 1fr));
      gap: 16px
    }

    .chap-card {
      position: relative;
      border: 1px solid var(--line);
      border-radius: var(--r);
      overflow: hidden;
      background: var(--panel);
      padding: 22px 20px 18px;
      text-align: left;
      transition: .2s;
    }

    .chap-card:hover {
      transform: translateY(-4px);
      border-color: var(--cc);
      box-shadow: 0 18px 40px -20px var(--cc)
    }

    .chap-card .tag {
      position: absolute;
      top: 0;
      left: 22px;
      background: var(--cc);
      color: #10130d;
      font-size: 10.5px;
      font-weight: 800;
      letter-spacing: .1em;
      padding: 4px 10px;
      border-radius: 0 0 8px 8px;
      text-transform: uppercase
    }

    .chap-card .glyph {
      font-size: 34px;
      margin: 14px 0 10px;
      filter: saturate(1.1)
    }

    .chap-card h4 {
      font-family: var(--serif);
      font-size: 20px;
      font-weight: 600;
      line-height: 1.08
    }

    .chap-card .sub {
      font-size: 12.5px;
      color: var(--ink-dim);
      margin-top: 4px
    }

    .chap-card .meter {
      height: 6px;
      border-radius: 99px;
      background: var(--bg);
      margin-top: 16px;
      overflow: hidden
    }

    .chap-card .meter i {
      display: block;
      height: 100%;
      background: var(--cc);
      width: 0;
      transition: width .6s
    }

    .chap-card .pct {
      display: flex;
      justify-content: space-between;
      font-size: 11px;
      color: var(--ink-faint);
      margin-top: 7px;
      font-family: var(--mono)
    }

    /* ---------- Mode grid ---------- */
    .modes {
      display: grid;
      grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
      gap: 14px
    }

    .mode-card {
      border: 1px solid var(--line);
      border-radius: var(--r);
      background: var(--panel);
      padding: 20px;
      text-align: left;
      transition: .18s;
      display: flex;
      flex-direction: column;
      gap: 6px;
      min-height: 140px
    }

    .mode-card:hover {
      transform: translateY(-3px);
      border-color: var(--c);
      background: var(--panel2)
    }

    .mode-card .mi {
      font-size: 26px
    }

    .mode-card h4 {
      font-family: var(--serif);
      font-size: 18px;
      font-weight: 600
    }

    .mode-card p {
      font-size: 12.5px;
      color: var(--ink-dim);
      flex: 1
    }

    .mode-card .go {
      font-size: 11px;
      font-weight: 700;
      letter-spacing: .1em;
      text-transform: uppercase;
      color: var(--c)
    }

    /* ---------- Buttons ---------- */
    .btn {
      display: inline-flex;
      align-items: center;
      gap: 8px;
      padding: 11px 20px;
      border-radius: 11px;
      font-weight: 700;
      font-size: 14px;
      transition: .16s;
      border: 1px solid transparent
    }

    .btn-primary {
      background: linear-gradient(135deg, var(--c), var(--c-d));
      color: #15110a
    }

    .btn-primary:hover {
      filter: brightness(1.08);
      transform: translateY(-1px)
    }

    .btn-ghost {
      border-color: var(--line2);
      color: var(--ink);
      background: var(--panel)
    }

    .btn-ghost:hover {
      border-color: var(--c);
      color: var(--c)
    }

    .btn-sm {
      padding: 8px 14px;
      font-size: 12.5px;
      border-radius: 9px
    }

    .back-link {
      display: inline-flex;
      align-items: center;
      gap: 7px;
      color: var(--ink-dim);
      font-size: 13px;
      font-weight: 600;
      margin-bottom: 18px;
      transition: .15s
    }

    .back-link:hover {
      color: var(--c)
    }

    /* ---------- View header ---------- */
    .view-head {
      display: flex;
      align-items: flex-end;
      justify-content: space-between;
      gap: 16px;
      flex-wrap: wrap;
      margin-bottom: 6px
    }

    .view-head .t .chip {
      display: inline-block;
      font-size: 10.5px;
      font-weight: 800;
      letter-spacing: .1em;
      text-transform: uppercase;
      color: var(--c);
      border: 1px solid var(--c);
      border-radius: 6px;
      padding: 2px 9px;
      margin-bottom: 10px
    }

    .view-head .t h2 {
      font-family: var(--serif);
      font-size: clamp(26px, 5vw, 38px);
      font-weight: 600;
      line-height: 1
    }

    .view-head .t p {
      color: var(--ink-dim);
      font-size: 14px;
      margin-top: 7px;
      max-width: 480px
    }

    /* ---------- Notes ---------- */
    .notes-wrap {
      display: grid;
      grid-template-columns: 200px 1fr;
      gap: 26px;
      margin-top: 26px;
      align-items: start;
      /* Prevent any child from blowing out the grid column */
      min-width: 0;
    }
    .notes-wrap > div {
      min-width: 0;   /* critical — allows children to shrink below intrinsic size */
      overflow: hidden;
    }

    .notes-toc {
      position: sticky;
      top: 78px;
      border: 1px solid var(--line);
      border-radius: var(--r);
      background: var(--panel);
      padding: 14px;
      font-size: 13px
    }

    .notes-toc b {
      display: block;
      font-size: 10.5px;
      letter-spacing: .14em;
      text-transform: uppercase;
      color: var(--ink-faint);
      margin-bottom: 10px
    }

    .notes-toc a {
      display: block;
      padding: 6px 9px;
      border-radius: 8px;
      color: var(--ink-dim);
      cursor: pointer;
      transition: .13s;
      border-left: 2px solid transparent
    }

    .notes-toc a:hover,
    .notes-toc a.active {
      color: var(--ink);
      background: var(--bg);
      border-left-color: var(--c)
    }

    .note-sec {
      background: var(--paper);
      color: var(--paper-ink);
      border-radius: var(--r);
      padding: 26px 28px;
      margin-bottom: 18px;
      scroll-margin-top: 80px;
      box-shadow: var(--shadow)
    }

    .note-sec h3 {
      font-family: var(--serif);
      font-size: 23px;
      font-weight: 600;
      color: var(--paper-ink);
      margin-bottom: 4px;
      display: flex;
      align-items: center;
      gap: 10px
    }

    .note-sec h3 .num {
      font-family: var(--mono);
      font-size: 12px;
      background: var(--c);
      color: #15110a;
      border-radius: 6px;
      padding: 3px 8px;
      font-weight: 600
    }

    .note-sec h4 {
      font-family: var(--serif);
      font-size: 16.5px;
      font-weight: 600;
      margin: 20px 0 7px;
      color: var(--anat-d);
    }

    .note-sec p {
      margin: 9px 0;
      color: #34402f;
      font-size: 14.5px
    }

    .note-sec ul,
    .note-sec ol {
      margin: 8px 0 8px 4px;
      padding-left: 20px
    }

    .note-sec li {
      margin: 5px 0;
      color: #34402f;
      font-size: 14.3px
    }

    .note-sec b,
    .note-sec strong {
      color: #1c241a
    }

    .note-sec em {
      color: var(--anat-d);
      font-style: italic
    }

    .kw {
      background: #efe7d0;
      border-bottom: 2px solid var(--gold);
      padding: 0 3px;
      border-radius: 3px;
      font-weight: 600
    }

    /* Tables: always scrollable horizontally on any screen size */
    .note-sec {
      background: var(--paper);
      color: var(--paper-ink);
      border-radius: var(--r);
      padding: 26px 28px;
      margin-bottom: 18px;
      scroll-margin-top: 80px;
      box-shadow: var(--shadow);
      /* Let the note section itself shrink on mobile */
      min-width: 0;
      overflow: hidden;
    }

    /* Wrap tables in a scrollable container */
    .note-sec table.cmp {
      display: block;
      overflow-x: auto;
      -webkit-overflow-scrolling: touch;
      white-space: nowrap; /* prevent cell text wrapping that causes layout explosion */
    }
    /* But let cells wrap once inside the scrollable block */
    .note-sec table.cmp th,
    .note-sec table.cmp td {
      white-space: normal;
      min-width: 100px;
    }

    table.cmp {
      width: 100%;
      border-collapse: collapse;
      margin: 14px 0;
      font-size: 13.3px;
      background: #fff;
      border-radius: 10px;
      overflow: hidden;
      box-shadow: 0 2px 8px rgba(0, 0, 0, .06)
    }

    table.cmp th {
      background: var(--paper-ink);
      color: var(--paper);
      padding: 9px 11px;
      text-align: left;
      font-weight: 600;
      font-size: 12.5px
    }

    table.cmp td {
      padding: 8px 11px;
      border-top: 1px solid var(--paper-line);
      color: #34402f;
      vertical-align: top
    }

    table.cmp tr:nth-child(even) td {
      background: #efe9da
    }

    .flow {
      display: flex;
      flex-wrap: wrap;
      align-items: center;
      gap: 8px;
      margin: 14px 0;
      padding: 14px;
      background: #efe9da;
      border-radius: 10px;
      border: 1px dashed var(--paper-line)
    }

    .flow .node {
      background: #fff;
      border: 1px solid var(--paper-line);
      border-radius: 8px;
      padding: 7px 12px;
      font-size: 12.8px;
      font-weight: 600;
      color: #2a3326
    }

    .flow .arr {
      color: var(--gold-deep);
      font-weight: 900
    }

    .formula {
      font-family: var(--mono);
      background: #2a3326;
      color: #f6f1e4;
      padding: 12px 16px;
      border-radius: 10px;
      margin: 12px 0;
      font-size: 13.5px;
      display: block;
      overflow-x: auto
    }

    .formula .hl {
      color: var(--gold)
    }

    .callout {
      border-left: 4px solid var(--gold);
      background: #efe7cf;
      padding: 11px 15px;
      border-radius: 0 10px 10px 0;
      margin: 13px 0;
      font-size: 13.6px;
      color: #3a3324
    }

    .callout b {
      color: #5a4a1c
    }

    /* ---------- Mnemonics ---------- */
    .mnem-grid {
      display: grid;
      grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
      gap: 16px;
      margin-top: 24px
    }

    .mnem {
      border: 1px solid var(--line);
      border-radius: var(--r);
      background: linear-gradient(160deg, var(--panel2), var(--panel));
      padding: 20px;
      position: relative;
      overflow: hidden
    }

    .mnem::before {
      content: "🧠";
      position: absolute;
      right: -8px;
      top: -8px;
      font-size: 54px;
      opacity: .07
    }

    .mnem h4 {
      font-family: var(--serif);
      font-size: 16px;
      font-weight: 600;
      margin-bottom: 8px;
      color: var(--gold)
    }

    .mnem .device {
      font-family: var(--serif);
      font-size: 19px;
      font-weight: 600;
      font-style: italic;
      color: var(--ink);
      line-height: 1.3;
      margin-bottom: 10px
    }

    .mnem .device b {
      color: var(--c);
      font-style: normal
    }

    .mnem .expand {
      font-size: 13px;
      color: var(--ink-dim)
    }

    .mnem .expand .row {
      display: flex;
      gap: 8px;
      margin: 4px 0
    }

    .mnem .expand .row .L {
      font-weight: 800;
      color: var(--c);
      font-family: var(--mono);
      flex: none;
      width: 18px
    }


    /* ---- Light-theme override: .mnem inside .note-sec (paper bg) ---- */
    .note-sec .mnem {
      background: #fff;
      border: 1.5px solid var(--paper-line);
      box-shadow: 0 2px 10px rgba(0,0,0,.06);
    }
    .note-sec .mnem::before {
      opacity: .04;
    }
    .note-sec .mnem h4 {
      color: #7f4ea0;
    }
    .note-sec .mnem .device {
      color: #1c241a;
      font-size: 17px;
    }
    .note-sec .mnem .device b {
      color: #7f4ea0;
    }
    .note-sec .mnem .expand {
      color: #3a402f;
    }
    .note-sec .mnem .expand .row .L {
      color: #7f4ea0;
    }
    /* ---------- Flashcards ---------- */
    .fc-stage {
      max-width: 560px;
      margin: 30px auto 0;
      text-align: center
    }

    .fc-progress {
      display: flex;
      justify-content: space-between;
      align-items: center;
      font-size: 13px;
      color: var(--ink-dim);
      margin-bottom: 14px;
      font-family: var(--mono)
    }

    .fc-bar {
      height: 6px;
      background: var(--panel);
      border-radius: 99px;
      overflow: hidden;
      margin-bottom: 20px
    }

    .fc-bar i {
      display: block;
      height: 100%;
      background: var(--c);
      width: 0;
      transition: .4s
    }

    .flashcard {
      perspective: 1600px;
      height: 300px;
      cursor: pointer
    }

    .fc-inner {
      position: relative;
      width: 100%;
      height: 100%;
      transition: transform .55s cubic-bezier(.4, .2, .2, 1);
      transform-style: preserve-3d
    }

    .flashcard.flip .fc-inner {
      transform: rotateY(180deg)
    }

    .fc-face {
      position: absolute;
      inset: 0;
      backface-visibility: hidden;
      border-radius: var(--r);
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      padding: 30px;
      box-shadow: var(--shadow)
    }

    .fc-front {
      background: var(--paper);
      color: var(--paper-ink)
    }

    .fc-back {
      background: linear-gradient(160deg, var(--panel2), var(--panel));
      border: 1px solid var(--c);
      transform: rotateY(180deg);
      color: var(--ink)
    }

    .fc-face .lab {
      font-size: 10.5px;
      letter-spacing: .18em;
      text-transform: uppercase;
      font-weight: 800;
      margin-bottom: 14px;
      opacity: .6
    }

    .fc-front .lab {
      color: var(--c-d)
    }

    .fc-back .lab {
      color: var(--c)
    }

    .fc-face .body {
      font-family: var(--serif);
      font-size: 21px;
      font-weight: 500;
      line-height: 1.34
    }

    .fc-back .body {
      font-family: var(--sans);
      font-size: 16px;
      font-weight: 500
    }

    .fc-face .hint {
      font-size: 12px;
      color: var(--paper-dim);
      margin-top: 14px;
      font-style: italic
    }

    .fc-tap {
      position: absolute;
      bottom: 12px;
      left: 0;
      right: 0;
      text-align: center;
      font-size: 11px;
      opacity: .5;
      letter-spacing: .1em
    }

    .fc-judge {
      display: flex;
      gap: 12px;
      justify-content: center;
      margin-top: 22px
    }

    .fc-actions {
      display: flex;
      justify-content: center;
      gap: 12px;
      margin-top: 18px;
      flex-wrap: wrap
    }

    .judge-btn {
      flex: 1;
      max-width: 200px;
      padding: 13px;
      border-radius: 12px;
      font-weight: 700;
      font-size: 14px;
      border: 1px solid
    }

    .judge-known {
      background: rgba(95, 194, 126, .12);
      border-color: var(--ok);
      color: var(--ok)
    }

    .judge-known:hover {
      background: rgba(95, 194, 126, .22)
    }

    .judge-again {
      background: rgba(233, 116, 95, .12);
      border-color: var(--bad);
      color: var(--bad)
    }

    .judge-again:hover {
      background: rgba(233, 116, 95, .22)
    }

    /* ---------- Active recall ---------- */
    .ar-stage {
      max-width: 620px;
      margin: 28px auto 0
    }

    .ar-card {
      border: 1px solid var(--line);
      border-radius: var(--r);
      background: var(--panel);
      padding: 24px
    }

    .ar-q {
      font-family: var(--serif);
      font-size: 21px;
      font-weight: 500;
      line-height: 1.35;
      margin-bottom: 6px
    }

    .ar-hint-btn {
      font-size: 12px;
      color: var(--c);
      font-weight: 700;
      margin-bottom: 14px;
      display: inline-block
    }

    .ar-hint {
      font-size: 13px;
      color: var(--ink-dim);
      background: var(--bg);
      border-radius: 8px;
      padding: 9px 12px;
      margin-bottom: 14px;
      border-left: 3px solid var(--c)
    }

    .ar-input {
      width: 100%;
      min-height: 120px;
      background: var(--bg);
      border: 1px solid var(--line2);
      border-radius: 12px;
      padding: 14px;
      color: var(--ink);
      font-family: inherit;
      font-size: 15px;
      resize: vertical
    }

    .ar-input:focus {
      outline: none;
      border-color: var(--c)
    }

    .ar-answer {
      margin-top: 16px;
      background: var(--paper);
      color: var(--paper-ink);
      border-radius: 12px;
      padding: 18px 20px
    }

    .ar-answer .lab {
      font-size: 10.5px;
      letter-spacing: .16em;
      text-transform: uppercase;
      font-weight: 800;
      color: var(--c-d);
      margin-bottom: 8px
    }

    .ar-answer .txt {
      font-size: 14.5px;
      line-height: 1.6;
      color: #34402f
    }

    .ar-answer .txt b {
      color: #1c241a
    }

    .self-grade {
      margin-top: 18px
    }

    .self-grade .lab {
      font-size: 12px;
      color: var(--ink-dim);
      text-align: center;
      margin-bottom: 10px
    }

    .grade-row {
      display: flex;
      gap: 10px;
      justify-content: center;
      flex-wrap: wrap
    }

    .grade-btn {
      padding: 10px 16px;
      border-radius: 10px;
      font-weight: 700;
      font-size: 13px;
      border: 1px solid var(--line2);
      background: var(--panel)
    }

    .grade-btn[data-g="0"]:hover {
      border-color: var(--bad);
      color: var(--bad)
    }

    .grade-btn[data-g="1"]:hover {
      border-color: var(--warn);
      color: var(--warn)
    }

    .grade-btn[data-g="2"]:hover {
      border-color: var(--ok);
      color: var(--ok)
    }

    /* ---------- Quiz / Boss MCQ ---------- */
    .quiz-stage {
      max-width: 640px;
      margin: 24px auto 0
    }

    .quiz-hud {
      display: flex;
      justify-content: space-between;
      align-items: center;
      margin-bottom: 8px;
      font-size: 13px
    }

    .quiz-hud .lives {
      letter-spacing: 2px
    }

    .quiz-hud .qnum {
      font-family: var(--mono);
      color: var(--ink-dim)
    }

    .quiz-hud .score {
      font-family: var(--mono);
      color: var(--c);
      font-weight: 600
    }

    .quiz-bar {
      height: 6px;
      background: var(--panel);
      border-radius: 99px;
      overflow: hidden;
      margin-bottom: 20px
    }

    .quiz-bar i {
      display: block;
      height: 100%;
      background: var(--c);
      transition: .3s
    }

    .timer-bar {
      height: 4px;
      background: var(--panel);
      border-radius: 99px;
      overflow: hidden;
      margin-bottom: 18px
    }

    .timer-bar i {
      display: block;
      height: 100%;
      background: var(--warn);
      width: 100%
    }

    .mcq-q {
      font-family: var(--serif);
      font-size: 20px;
      font-weight: 500;
      line-height: 1.34;
      margin-bottom: 20px
    }

    .mcq-opts {
      display: grid;
      gap: 11px
    }

    .opt {
      display: flex;
      align-items: center;
      gap: 13px;
      border: 1px solid var(--line2);
      border-radius: 12px;
      padding: 14px 16px;
      background: var(--panel);
      text-align: left;
      font-size: 14.5px;
      transition: .13s;
      width: 100%
    }

    .opt:hover:not(.locked) {
      border-color: var(--c);
      background: var(--panel2)
    }

    .opt .key {
      width: 26px;
      height: 26px;
      flex: none;
      border-radius: 7px;
      border: 1px solid var(--line2);
      display: grid;
      place-items: center;
      font-size: 13px;
      font-weight: 700;
      font-family: var(--mono)
    }

    .opt.correct {
      border-color: var(--ok);
      background: rgba(95, 194, 126, .14)
    }

    .opt.correct .key {
      background: var(--ok);
      color: #0e1c17;
      border-color: var(--ok)
    }

    .opt.wrong {
      border-color: var(--bad);
      background: rgba(233, 116, 95, .14)
    }

    .opt.wrong .key {
      background: var(--bad);
      color: #0e1c17;
      border-color: var(--bad)
    }

    .opt.locked {
      cursor: default
    }

    .mcq-explain {
      margin-top: 16px;
      border-radius: 12px;
      padding: 15px 17px;
      font-size: 13.8px;
      line-height: 1.55;
      display: none;
      border-left: 4px solid var(--c)
    }

    .mcq-explain.show {
      display: block
    }

    .mcq-explain.ok {
      background: rgba(95, 194, 126, .1);
      border-left-color: var(--ok)
    }

    .mcq-explain.no {
      background: rgba(233, 116, 95, .1);
      border-left-color: var(--bad)
    }

    .mcq-explain b {
      color: var(--c)
    }

    .mcq-next {
      margin-top: 18px;
      text-align: right
    }

    /* ---------- Match-up ---------- */
    .match-stage {
      max-width: 760px;
      margin: 22px auto 0
    }

    .match-hud {
      display: flex;
      justify-content: space-between;
      align-items: center;
      margin-bottom: 16px;
      font-size: 14px;
      font-family: var(--mono)
    }

    .match-hud .time {
      color: var(--warn)
    }

    .match-grid {
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 14px
    }

    .match-col {
      display: flex;
      flex-direction: column;
      gap: 10px
    }

    .match-col h5 {
      font-size: 11px;
      letter-spacing: .14em;
      text-transform: uppercase;
      color: var(--ink-faint);
      text-align: center;
      font-weight: 700
    }

    .tile {
      border: 1px solid var(--line2);
      border-radius: 11px;
      padding: 13px 14px;
      background: var(--panel);
      font-size: 13.8px;
      transition: .13s;
      text-align: left
    }

    .tile:hover:not(.matched) {
      border-color: var(--c)
    }

    .tile.sel {
      border-color: var(--c);
      background: var(--panel2);
      box-shadow: 0 0 0 2px var(--c) inset
    }

    .tile.matched {
      opacity: .32;
      border-style: dashed;
      cursor: default;
      pointer-events: none
    }

    .tile.miss {
      animation: shake .35s
    }

    @keyframes shake {

      0%,
      100% {
        transform: translateX(0)
      }

      25% {
        transform: translateX(-6px)
      }

      75% {
        transform: translateX(6px)
      }
    }

    /* ---------- Build the Pathway ---------- */
    .path-stage {
      max-width: 680px;
      margin: 22px auto 0
    }

    .path-prompt {
      border: 1px solid var(--line);
      background: var(--panel);
      border-radius: var(--r);
      padding: 18px 20px;
      margin-bottom: 18px
    }

    .path-prompt h4 {
      font-family: var(--serif);
      font-size: 18px;
      font-weight: 600;
      margin-bottom: 4px
    }

    .path-prompt p {
      font-size: 13.5px;
      color: var(--ink-dim)
    }

    .path-slots {
      display: flex;
      flex-direction: column;
      gap: 9px;
      margin-bottom: 18px
    }

    .slot {
      min-height: 50px;
      border: 1.5px dashed var(--line2);
      border-radius: 11px;
      display: flex;
      align-items: center;
      gap: 12px;
      padding: 8px 12px;
      transition: .13s
    }

    .slot .idx {
      width: 26px;
      height: 26px;
      flex: none;
      border-radius: 7px;
      background: var(--bg);
      display: grid;
      place-items: center;
      font-family: var(--mono);
      font-size: 12px;
      color: var(--ink-faint)
    }

    .slot.filled {
      border-style: solid;
      background: var(--panel)
    }

    .slot.ok {
      border-color: var(--ok);
      background: rgba(95, 194, 126, .1)
    }

    .slot.no {
      border-color: var(--bad);
      background: rgba(233, 116, 95, .1)
    }

    .slot .chiptxt {
      font-size: 14px;
      font-weight: 600
    }

    .path-pool {
      display: flex;
      flex-wrap: wrap;
      gap: 9px;
      padding: 14px;
      border: 1px dashed var(--line);
      border-radius: var(--r);
      background: var(--bg2);
      min-height: 60px
    }

    .pchip {
      border: 1px solid var(--line2);
      border-radius: 9px;
      padding: 9px 14px;
      background: var(--panel);
      font-size: 13.5px;
      font-weight: 600;
      transition: .13s
    }

    .pchip:hover {
      border-color: var(--c);
      transform: translateY(-2px)
    }

    .pchip.used {
      display: none
    }

    /* ---------- Result / completion ---------- */
    .result {
      max-width: 520px;
      margin: 40px auto 0;
      text-align: center;
      border: 1px solid var(--line);
      background: var(--panel);
      border-radius: var(--r);
      padding: 36px 30px
    }

    .result .big {
      font-size: 64px;
      margin-bottom: 8px
    }

    .result h3 {
      font-family: var(--serif);
      font-size: 30px;
      font-weight: 600
    }

    .result .scoreline {
      font-family: var(--mono);
      font-size: 18px;
      color: var(--c);
      margin: 12px 0
    }

    .result p {
      color: var(--ink-dim);
      font-size: 14px;
      margin-bottom: 20px
    }

    .result .actions {
      display: flex;
      gap: 12px;
      justify-content: center;
      flex-wrap: wrap
    }

    .ring {
      --p: 0;
      width: 120px;
      height: 120px;
      border-radius: 50%;
      margin: 0 auto 14px;
      display: grid;
      place-items: center;
      background: conic-gradient(var(--c) calc(var(--p)*1%), var(--panel2) 0)
    }

    .ring span {
      width: 92px;
      height: 92px;
      border-radius: 50%;
      background: var(--panel);
      display: grid;
      place-items: center;
      font-family: var(--mono);
      font-size: 26px;
      font-weight: 600
    }

    /* toast */
    .toast {
      position: fixed;
      bottom: 24px;
      left: 50%;
      transform: translateX(-50%) translateY(120px);
      background: var(--panel2);
      border: 1px solid var(--c);
      color: var(--ink);
      padding: 12px 20px;
      border-radius: 12px;
      font-size: 14px;
      font-weight: 600;
      z-index: 200;
      transition: .3s;
      box-shadow: var(--shadow)
    }

    .toast.show {
      transform: translateX(-50%) translateY(0)
    }

    .toast .xp {
      color: var(--gold);
      font-family: var(--mono)
    }

    footer {
      text-align: center;
      padding: 30px 20px;
      color: var(--ink-faint);
      font-size: 12px;
      border-top: 1px solid var(--line);
      margin-top: 40px
    }

    footer b {
      color: var(--ink-dim)
    }

    @media (max-width: 760px) {
      /* Notes: stack TOC above content */
      .notes-wrap {
        grid-template-columns: 1fr;
      }
      .notes-wrap > div {
        overflow: visible; /* allow normal flow when stacked */
      }
      .notes-toc {
        position: static;
        display: flex;
        flex-wrap: wrap;
        gap: 4px;
        overflow-x: auto;
        -webkit-overflow-scrolling: touch;
        padding-bottom: 8px;
      }
      .notes-toc b {
        width: 100%;
      }
      .notes-toc a {
        flex: none;
        min-width: auto;
        text-align: center;
        border-left: none;
        border-bottom: 2px solid transparent;
        font-size: 12px;
        padding: 5px 10px;
        white-space: nowrap;
      }
      /* Note sections: tighter padding on mobile */
      .note-sec {
        padding: 18px 16px;
        border-radius: 12px;
      }
      .note-sec h3 {
        font-size: 18px;
      }
      .note-sec h4 {
        font-size: 15px;
      }
      .note-sec p,
      .note-sec li {
        font-size: 13.5px;
      }
      /* Flow diagrams wrap nicely */
      .flow {
        padding: 10px;
        gap: 6px;
      }
      .flow .step, .flow .node {
        font-size: 11.5px;
        padding: 5px 9px;
      }
      /* Callouts */
      .callout {
        font-size: 13px;
        padding: 9px 12px;
      }
      /* Brand font size in the 760px range */
      .brand h1 {
        font-size: 15px;
      }
      /* Match game grid */
      .match-grid {
        gap: 9px;
      }
      .tile {
        font-size: 12.5px;
        padding: 11px;
      }
      /* Mnemonic grid */
      .mnem-grid {
        grid-template-columns: 1fr;
      }
      /* View head on mobile */
      .view-head {
        flex-direction: column;
        align-items: flex-start;
        gap: 10px;
      }
      /* Flashcard stage */
      .fc-stage {
        padding: 0;
      }
      .flashcard {
        min-height: 200px;
      }
      /* Quiz */
      .mcq-opts {
        gap: 8px;
      }
      .opt {
        font-size: 13px;
        padding: 11px 13px;
      }
      /* Pathway */
      .path-stage {
        padding: 0;
      }
      .pchip {
        font-size: 12px;
        padding: 7px 11px;
      }
    }

    .fade {
      animation: fade .35s ease
    }

    @keyframes fade {
      from {
        opacity: 0;
        transform: translateY(8px)
      }

      to {
        opacity: 1;
        transform: none
      }
    }

    .pop {
      animation: pop .3s ease
    }

    @keyframes pop {
      0% {
        transform: scale(.96);
        opacity: 0
      }

      100% {
        transform: scale(1);
        opacity: 1
      }
    }
  
    /* ---------- Footer ---------- */
    .site-footer {
      border-top: 1px solid var(--line);
      background: var(--bg2);
      padding: 50px clamp(14px, 4vw, 40px) 30px;
      margin-top: 80px;
      color: var(--ink-dim);
    }
    .footer-content {
      max-width: 1080px;
      margin: 0 auto;
      display: flex;
      flex-wrap: wrap;
      justify-content: space-between;
      gap: 30px;
    }
    .footer-brand {
      display: flex;
      gap: 14px;
      align-items: center;
      max-width: 300px;
    }
    .footer-brand .mark {
      width: 44px;
      height: 44px;
      border-radius: 12px;
      display: grid;
      place-items: center;
      background: linear-gradient(135deg, var(--gold), var(--gold-deep));
      color: #1a130a;
      font-family: var(--serif);
      font-weight: 900;
      font-size: 22px;
      box-shadow: 0 6px 18px -6px var(--gold-deep);
    }
    .brand-text h3 {
      font-family: var(--serif);
      font-size: 20px;
      color: var(--ink);
      line-height: 1.1;
    }
    .brand-text p {
      font-size: 13px;
      color: var(--gold);
      margin-top: 4px;
    }
    .footer-links {
      display: flex;
      gap: 60px;
      flex-wrap: wrap;
    }
    .link-col h4 {
      font-size: 13px;
      text-transform: uppercase;
      letter-spacing: 0.1em;
      color: var(--ink);
      margin-bottom: 14px;
    }
    .link-col a {
      display: block;
      font-size: 14px;
      color: var(--ink-dim);
      text-decoration: none;
      margin-bottom: 10px;
      transition: color 0.2s;
    }
    .link-col a:hover {
      color: var(--gold);
    }
    .footer-bottom {
      max-width: 1080px;
      margin: 40px auto 0;
      padding-top: 20px;
      border-top: 1px solid var(--line);
      display: flex;
      flex-wrap: wrap;
      justify-content: space-between;
      gap: 14px;
      font-size: 12.5px;
      color: var(--ink-faint);
    }
    @media (max-width: 600px) {
      .footer-content {
        flex-direction: column;
      }
      .footer-links {
        gap: 30px;
      }
    }

    /* ---------- Hero h1 (updated to h1 for SEO) ---------- */
    .hero h1 {
      font-family: var(--serif);
      font-weight: 900;
      font-size: clamp(34px, 7vw, 62px);
      line-height: .98;
      letter-spacing: -.02em;
    }
    .hero h1 em {
      font-style: italic;
      font-weight: 500;
      color: var(--gold);
    }

    /* ---------- Subject Filter Bar ---------- */
    .filter-bar {
      display: flex;
      align-items: center;
      gap: 14px;
      margin: 28px 0 0;
      flex-wrap: wrap;
    }

    .subject-tabs {
      display: flex;
      gap: 8px;
      flex-wrap: wrap;
      flex: 1;
    }

    .subject-tab {
      padding: 8px 15px;
      border-radius: 999px;
      border: 1px solid var(--line2);
      background: var(--panel);
      color: var(--ink-dim);
      font-size: 13px;
      font-weight: 600;
      transition: .16s;
      white-space: nowrap;
    }
    .subject-tab:hover {
      border-color: var(--gold);
      color: var(--ink);
    }
    .subject-tab.active {
      background: var(--gold);
      color: #15110a;
      border-color: var(--gold);
      box-shadow: 0 4px 16px -6px var(--gold);
    }

    /* ---------- Search ---------- */
    .search-wrap {
      position: relative;
      min-width: 200px;
      flex: 0 0 220px;
    }
    .search-icon {
      position: absolute;
      left: 12px;
      top: 50%;
      transform: translateY(-50%);
      font-size: 14px;
      pointer-events: none;
      opacity: .5;
    }
    .search-input {
      width: 100%;
      padding: 9px 14px 9px 36px;
      border-radius: 999px;
      border: 1px solid var(--line2);
      background: var(--panel);
      color: var(--ink);
      font-family: var(--sans);
      font-size: 13.5px;
      outline: none;
      transition: .15s;
    }
    .search-input:focus {
      border-color: var(--gold);
      box-shadow: 0 0 0 3px rgba(226, 179, 95, .12);
    }
    .search-input::placeholder {
      color: var(--ink-faint);
    }
    /* Remove native search clear button styling issues */
    .search-input::-webkit-search-cancel-button { opacity: .4; cursor: pointer; }

    /* ---------- Chapter count in section label ---------- */
    .chap-count {
      font-family: var(--mono);
      font-size: 12px;
      color: var(--ink-faint);
      border: 1px solid var(--line);
      border-radius: 6px;
      padding: 2px 9px;
      white-space: nowrap;
    }

    /* ---------- Subject badges on chapter cards ---------- */
    .subject-badge {
      display: inline-block;
      font-size: 10px;
      font-weight: 800;
      letter-spacing: .1em;
      text-transform: uppercase;
      padding: 3px 9px;
      border-radius: 0 0 8px 8px;
      position: absolute;
      top: 0;
      left: 18px;
    }
    .badge-bio11 {
      background: #34d399;
      color: #052e16;
    }
    .badge-bio12 {
      background: #818cf8;
      color: #1e1b4b;
    }
    .badge-phy {
      background: #fbbf24;
      color: #451a03;
    }
    .badge-chem {
      background: #f472b6;
      color: #500724;
    }

    /* Make sure glyph clears the badge */
    .chap-card .glyph {
      margin-top: 22px;
    }

    /* ---------- Empty state ---------- */
    .empty-state {
      grid-column: 1 / -1;
      text-align: center;
      padding: 50px 20px;
      color: var(--ink-faint);
      font-size: 15px;
      border: 1px dashed var(--line2);
      border-radius: var(--r);
    }

    @media (max-width: 640px) {
      .filter-bar { flex-direction: column; align-items: stretch; }
      .search-wrap { flex: none; width: 100%; }
      .subject-tabs { gap: 6px; }
      .subject-tab { padding: 7px 12px; font-size: 12px; }
    }

    /* ---------- Load More button ---------- */
    .load-more-wrap {
      grid-column: 1 / -1;
      display: flex;
      justify-content: center;
      padding: 10px 0 4px;
    }
    .load-more-btn {
      min-width: 240px;
      justify-content: center;
      gap: 10px;
      border-style: dashed;
      font-size: 13.5px;
      letter-spacing: .02em;
      transition: .18s;
    }
    .load-more-btn:hover {
      border-color: var(--gold);
      color: var(--gold);
      background: rgba(226,179,95,.06);
    }