:root {
    --bg: #0e0e12;
    --surface: #16161d;
    --surface2: #1e1e28;
    --border: #2e2e3e;
    --text: #e8e8f0;
    --muted: #7878a0;
    --accent: #7c6af5;
    --accent2: #f5a623;
    --accent3: #4ecdc4;
    --accent4: #ff6b9d;
    --green: #52e3a2;
    --red: #ff5c7c;
    --code-bg: #0a0a10;
    --radius: 12px;
  }

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

  body {
    font-family: 'Fraunces', Georgia, serif;
    background: var(--bg);
    color: var(--text);
    min-height: 100vh;
    line-height: 1.7;
  }

  /* ── Layout ── */
  .hero {
    text-align: center;
    padding: 64px 24px 48px;
    position: relative;
    overflow: hidden;
  }
  .hero::before {
    content: '';
    position: absolute;
    inset: 0;
    background: radial-gradient(ellipse 80% 60% at 50% 0%, #7c6af520 0%, transparent 70%);
    pointer-events: none;
  }
  .hero h1 {
    font-size: clamp(2.4rem, 6vw, 4.2rem);
    font-weight: 700;
    letter-spacing: -0.03em;
    line-height: 1.1;
  }
  .hero h1 code {
    color: var(--accent);
    font-family: 'JetBrains Mono', monospace;
  }
  .hero p {
    max-width: 560px;
    margin: 16px auto 0;
    color: var(--muted);
    font-size: 1.1rem;
    font-style: italic;
  }
  .badge {
    display: inline-block;
    background: #7c6af520;
    border: 1px solid #7c6af540;
    color: var(--accent);
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.72rem;
    padding: 4px 12px;
    border-radius: 100px;
    margin-bottom: 20px;
    letter-spacing: 0.08em;
    text-transform: uppercase;
  }

  main {
    max-width: 860px;
    margin: 0 auto;
    padding: 0 24px 80px;
  }

  /* ── Section headers ── */
  .section-label {
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.7rem;
    text-transform: uppercase;
    letter-spacing: 0.18em;
    color: var(--accent);
    margin-bottom: 8px;
  }
  h2 {
    font-size: 1.8rem;
    font-weight: 700;
    margin-bottom: 12px;
    line-height: 1.2;
  }
  h3 {
    font-size: 1.1rem;
    font-weight: 700;
    font-family: 'JetBrains Mono', monospace;
    color: var(--accent2);
    margin-bottom: 8px;
  }
  p { color: #b0b0c8; margin-bottom: 12px; }

  /* ── Lesson cards ── */
  .lesson {
    background: var(--surface);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 28px;
    margin-bottom: 28px;
    position: relative;
  }
  .lesson-num {
    position: absolute;
    top: -14px;
    left: 24px;
    background: var(--accent);
    color: #fff;
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.72rem;
    font-weight: 700;
    padding: 3px 12px;
    border-radius: 100px;
    letter-spacing: 0.06em;
  }

  /* ── Code blocks ── */
  .code-block {
    background: var(--code-bg);
    border: 1px solid var(--border);
    border-radius: 8px;
    padding: 18px 20px;
    margin: 14px 0;
    overflow-x: auto;
    position: relative;
  }
  .code-block pre {
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.82rem;
    line-height: 1.7;
    white-space: pre;
  }
  .kw   { color: #c792ea; }
  .fn   { color: #82aaff; }
  .val  { color: var(--accent3); }
  .prop { color: var(--accent2); }
  .cm   { color: var(--muted); font-style: italic; }
  .str  { color: var(--green); }

  .syntax-pill {
    background: #7c6af515;
    border: 1px dashed #7c6af550;
    border-radius: 8px;
    padding: 16px 20px;
    margin: 14px 0;
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.82rem;
    line-height: 1.9;
    color: #d0d0e8;
  }
  .syntax-pill .part { display: inline-block; padding: 1px 8px; border-radius: 4px; margin: 2px; }
  .part-prop { background: #f5a62322; color: var(--accent2); }
  .part-cond { background: #7c6af522; color: #a89df7; }
  .part-val  { background: #4ecdc422; color: var(--accent3); }
  .part-else { background: #ff6b9d22; color: var(--accent4); }
  .part-sep  { color: var(--muted); }

  /* ── Live demos ── */
  .demo-wrap {
    background: var(--surface2);
    border: 1px solid var(--border);
    border-radius: 8px;
    padding: 20px;
    margin-top: 16px;
  }
  .demo-label {
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.68rem;
    text-transform: uppercase;
    letter-spacing: 0.12em;
    color: var(--muted);
    margin-bottom: 12px;
  }

  /* ── Demo 1: style() color theme ── */
  #demo1-box {
    --theme: light;
    width: 100%;
    padding: 20px 24px;
    border-radius: 8px;
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.85rem;
    text-align: center;
    font-weight: 600;
    background: if(style(--theme: dark): #1a1a2e; else: #f0f4ff;);
    color: if(style(--theme: dark): #e0e0ff; else: #2233aa;);
    border: 2px solid if(style(--theme: dark): #4444aa; else: #aabbff;);
    /* Note: if(style()) switches are discrete — CSS transitions won't animate between states */
  }
  .toggle-row {
    display: flex; gap: 8px; flex-wrap: wrap; margin-top: 12px;
  }
  .demo-btn {
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.75rem;
    padding: 6px 14px;
    border-radius: 6px;
    border: 1px solid var(--border);
    background: var(--surface);
    color: var(--text);
    cursor: pointer;
    transition: border-color 0.2s, background 0.2s;
  }
  .demo-btn:hover { border-color: var(--accent); background: #7c6af510; }
  .demo-btn.active { border-color: var(--accent); background: var(--accent); color: #fff; }

  /* ── Demo 2: style() size ── */
  #demo2-box {
    --size: md;
    display: inline-block;
    padding: if(style(--size: sm): 6px 12px; style(--size: md): 12px 24px; else: 20px 40px;);
    font-size: if(style(--size: sm): 0.75rem; style(--size: md): 1rem; else: 1.4rem;);
    border-radius: if(style(--size: sm): 4px; style(--size: md): 8px; else: 14px;);
    background: var(--accent);
    color: #fff;
    font-family: 'JetBrains Mono', monospace;
    font-weight: 700;
    transition: all 0.2s;
    cursor: default;
  }

  /* ── Demo 3: media() ── */
  .media-demo-box {
    padding: 16px 20px;
    border-radius: 8px;
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.85rem;
    font-weight: 600;
    text-align: center;
    background: if(media(max-width: 600px): #ff6b9d20; else: #52e3a220;);
    border: 2px solid if(media(max-width: 600px): var(--accent4); else: var(--green););
    color: if(media(max-width: 600px): var(--accent4); else: var(--green););
  }

  /* ── Demo 4: supports() ── */
  .supports-demo {
    padding: 16px 20px;
    border-radius: 8px;
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.85rem;
    font-weight: 600;
    text-align: center;
    background: if(supports(display: grid): #7c6af522; else: #f5a62322;);
    border: 2px solid if(supports(display: grid): var(--accent); else: var(--accent2););
    color: if(supports(display: grid): var(--accent); else: var(--accent2););
  }

  /* ── Quiz section ── */
  .quiz-section {
    margin-top: 60px;
    padding-top: 40px;
    border-top: 1px solid var(--border);
  }
  .quiz-card {
    background: var(--surface);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 28px;
    margin-bottom: 24px;
    transition: border-color 0.2s;
  }
  .quiz-card.correct { border-color: var(--green); }
  .quiz-card.wrong   { border-color: var(--red); }

  .quiz-q {
    font-size: 1rem;
    font-weight: 600;
    margin-bottom: 6px;
    color: var(--text);
  }
  .quiz-hint {
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.78rem;
    color: var(--muted);
    margin-bottom: 16px;
  }
  .options {
    display: flex; flex-direction: column; gap: 8px;
  }
  .opt {
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.78rem;
    padding: 10px 14px;
    border-radius: 6px;
    border: 1px solid var(--border);
    background: var(--surface2);
    color: var(--text);
    cursor: pointer;
    text-align: left;
    transition: all 0.15s;
  }
  .opt:hover:not([disabled]) { border-color: var(--accent); background: #7c6af510; }
  .opt.correct-ans { border-color: var(--green); background: #52e3a215; color: var(--green); }
  .opt.wrong-ans   { border-color: var(--red);   background: #ff5c7c15; color: var(--red); }

  .feedback {
    margin-top: 12px;
    font-size: 0.85rem;
    padding: 10px 14px;
    border-radius: 6px;
    display: none;
  }
  .feedback.show { display: block; }
  .feedback.ok  { background: #52e3a215; color: var(--green); border: 1px solid #52e3a230; }
  .feedback.bad { background: #ff5c7c15; color: var(--red);   border: 1px solid #ff5c7c30; }

  /* ── Score bar ── */
  .score-wrap {
    background: var(--surface);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 24px;
    text-align: center;
    margin-top: 24px;
  }
  .score-num {
    font-size: 3rem;
    font-weight: 700;
    color: var(--accent);
    font-family: 'JetBrains Mono', monospace;
    line-height: 1;
  }
  .score-label { color: var(--muted); font-size: 0.85rem; margin-top: 6px; }
  .progress-bar {
    height: 6px;
    background: var(--border);
    border-radius: 100px;
    margin-top: 16px;
    overflow: hidden;
  }
  .progress-fill {
    height: 100%;
    background: linear-gradient(90deg, var(--accent), var(--accent3));
    border-radius: 100px;
    width: 0%;
    transition: width 0.5s cubic-bezier(.22,1,.36,1);
  }

  /* ── Cheatsheet ── */
  .cheatsheet {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
    gap: 14px;
    margin-top: 16px;
  }
  .cheat-card {
    background: var(--surface2);
    border: 1px solid var(--border);
    border-radius: 8px;
    padding: 16px;
  }
  .cheat-card h4 {
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.78rem;
    color: var(--accent);
    margin-bottom: 8px;
    text-transform: uppercase;
    letter-spacing: 0.1em;
  }
  .cheat-card p { font-size: 0.82rem; color: var(--muted); margin: 0; }

  /* ── Callout ── */
  .callout {
    border-left: 3px solid var(--accent2);
    padding: 12px 16px;
    background: #f5a62310;
    border-radius: 0 8px 8px 0;
    margin: 14px 0;
    font-size: 0.88rem;
    color: #d4a060;
  }
  .callout strong { color: var(--accent2); }

  /* ── Comparison table ── */
  table {
    width: 100%;
    border-collapse: collapse;
    font-size: 0.82rem;
    font-family: 'JetBrains Mono', monospace;
    margin: 14px 0;
  }
  th {
    background: var(--surface2);
    color: var(--accent);
    padding: 10px 14px;
    text-align: left;
    font-size: 0.72rem;
    text-transform: uppercase;
    letter-spacing: 0.1em;
    border-bottom: 1px solid var(--border);
  }
  td {
    padding: 10px 14px;
    border-bottom: 1px solid var(--border);
    color: #c0c0d8;
    vertical-align: top;
  }
  tr:last-child td { border-bottom: none; }
  tr:hover td { background: #ffffff05; }

  /* ── Responsive ── */
  @media (max-width: 600px) {
    .hero { padding: 40px 16px 32px; }
    main { padding: 0 16px 60px; }
    .lesson { padding: 22px 18px; }
  }

  /* ── Status card demo ── */
  .status-card {
    --status: inactive;
    padding: 12px 18px;
    border-radius: 8px;
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.78rem;
    font-weight: 700;
    border: 2px solid;
    cursor: pointer;
    border-color: if(
      style(--status: pending): royalblue;
      style(--status: complete): seagreen;
      else: gray
    );
    background-color: if(
      style(--status: pending): #eff7fa;
      style(--status: complete): #f6fff6;
      else: #f7f7f7
    );
    color: if(
      style(--status: pending): royalblue;
      style(--status: complete): seagreen;
      else: gray
    );
  }


  .support-note {
    display: flex;
    align-items: center;
    gap: 10px;
    padding: 12px 16px;
    background: #f5a62312;
    border: 1px solid #f5a62330;
    border-radius: 8px;
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.75rem;
    color: var(--accent2);
    margin-bottom: 28px;
  }
  .dot { width: 8px; height: 8px; border-radius: 50%; background: var(--accent2); flex-shrink: 0; }