:root {
    --bg: #F4EFE6;
    --bg-card: #FBF8F2;
    --ink: #1A1814;
    --ink-soft: #4A453D;
    --ink-muted: #8C8578;
    --accent: #B8412C;
    --accent-deep: #8A2F1F;
    --accent-soft: #E8D5CC;
    --rule: #1A1814;
    --grid: #D9D2C4;
    --code-bg: #1F1D1A;
  }

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

  html { scroll-behavior: smooth; }

  body {
    background: var(--bg);
    color: var(--ink);
    font-family: 'Inter Tight', sans-serif;
    font-size: 15px;
    line-height: 1.6;
    -webkit-font-smoothing: antialiased;
    background-image: radial-gradient(circle at 1px 1px, rgba(26,24,20,0.04) 1px, transparent 0);
    background-size: 24px 24px;
    min-height: 100vh;
  }

  .wrapper {
    max-width: 1280px;
    margin: 0 auto;
    padding: 32px 24px 120px;
  }

  /* ===== Masthead ===== */
  .masthead {
    border-top: 3px solid var(--rule);
    border-bottom: 1px solid var(--rule);
    padding: 20px 0 16px;
    display: flex;
    justify-content: space-between;
    align-items: baseline;
    flex-wrap: wrap;
    gap: 16px;
  }

  .masthead .edition,
  .masthead .date {
    font-family: 'JetBrains Mono', monospace;
    font-size: 11px;
    letter-spacing: 0.12em;
    text-transform: uppercase;
    color: var(--ink-soft);
  }

  .masthead-back,
  .masthead-demo {
    font-family: 'JetBrains Mono', monospace;
    font-size: 11px;
    letter-spacing: 0.12em;
    text-transform: uppercase;
    color: var(--accent);
    text-decoration: none;
  }

  .masthead-back:hover,
  .masthead-demo:hover {
    color: var(--accent-deep);
  }

  .title-block {
    text-align: center;
    padding: 56px 0 40px;
    border-bottom: 1px solid var(--rule);
    margin-bottom: 48px;
  }

  .title-block .kicker {
    font-family: 'JetBrains Mono', monospace;
    font-size: 11px;
    letter-spacing: 0.24em;
    text-transform: uppercase;
    color: var(--accent);
    margin-bottom: 18px;
  }

  .title-block h1 {
    font-family: 'Fraunces', serif;
    font-weight: 300;
    font-size: clamp(44px, 7.5vw, 96px);
    line-height: 0.95;
    letter-spacing: -0.03em;
    font-variation-settings: 'opsz' 144;
  }

  .title-block h1 em {
    font-style: italic;
    font-weight: 400;
    color: var(--accent);
  }

  .title-block .dek {
    font-family: 'Fraunces', serif;
    font-style: italic;
    font-weight: 400;
    font-size: 19px;
    color: var(--ink-soft);
    margin-top: 22px;
    max-width: 620px;
    margin-left: auto;
    margin-right: auto;
  }

  /* ===== Layout ===== */
  .layout {
    display: grid;
    grid-template-columns: 260px 1fr;
    gap: 48px;
    align-items: start;
  }

  @media (max-width: 900px) {
    .layout { grid-template-columns: 1fr; gap: 32px; }
  }

  /* ===== Sidebar ===== */
  .sidebar {
    position: sticky;
    top: 24px;
    z-index: 10;
    background: var(--bg-card);
    border: 1px solid var(--rule);
    padding: 24px 0 12px;
  }

  @media (max-width: 900px) {
    .sidebar { position: static; }
  }

  .sidebar-title {
    font-family: 'JetBrains Mono', monospace;
    font-size: 10px;
    letter-spacing: 0.2em;
    text-transform: uppercase;
    color: var(--ink-muted);
    padding: 0 24px 16px;
    border-bottom: 1px solid var(--grid);
    display: flex;
    justify-content: space-between;
  }

  .progress-track {
    height: 2px;
    background: var(--grid);
    margin: 0 24px 18px;
    position: relative;
    margin-top: 18px;
  }

  .progress-fill {
    height: 100%;
    background: var(--accent);
    width: 0%;
    transition: width 0.4s ease;
  }

  .progress-label {
    padding: 0 24px 16px;
    font-family: 'JetBrains Mono', monospace;
    font-size: 10px;
    letter-spacing: 0.16em;
    text-transform: uppercase;
    color: var(--ink-soft);
    border-bottom: 1px solid var(--grid);
    margin-bottom: 12px;
  }

  .progress-label span {
    color: var(--accent);
  }

  .toc {
    list-style: none;
  }

  .toc li {
    border-bottom: 1px solid var(--grid);
  }

  .toc li:last-child { border-bottom: none; }

  .toc a {
    display: flex;
    align-items: center;
    gap: 12px;
    padding: 12px 24px;
    text-decoration: none;
    color: var(--ink-soft);
    font-family: 'Inter Tight', sans-serif;
    font-size: 13px;
    line-height: 1.4;
    transition: background 0.15s, color 0.15s;
  }

  .toc a:hover {
    background: rgba(184, 65, 44, 0.06);
    color: var(--ink);
  }

  .toc a.active {
    background: rgba(184, 65, 44, 0.08);
    color: var(--accent);
    font-weight: 500;
  }

  .toc-num {
    font-family: 'JetBrains Mono', monospace;
    font-size: 10px;
    color: var(--ink-muted);
    min-width: 18px;
    letter-spacing: 0.05em;
  }

  .toc-check {
    margin-left: auto;
    width: 14px;
    height: 14px;
    border: 1px solid var(--grid);
    border-radius: 50%;
    flex-shrink: 0;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all 0.2s;
  }

  .toc li.done .toc-check {
    background: var(--accent);
    border-color: var(--accent);
  }

  .toc li.done .toc-check::after {
    content: '✓';
    color: white;
    font-size: 9px;
    font-weight: bold;
  }

  /* ===== Main ===== */
  main {
    min-width: 0;
  }

  .step {
    margin-bottom: 56px;
    padding-bottom: 48px;
    border-bottom: 1px solid var(--grid);
    scroll-margin-top: 24px;
  }

  .step:last-child { border-bottom: none; }

  .step-header {
    display: flex;
    align-items: baseline;
    gap: 18px;
    margin-bottom: 20px;
    padding-bottom: 16px;
    border-bottom: 1px solid var(--rule);
  }

  .step-num {
    font-family: 'JetBrains Mono', monospace;
    font-size: 11px;
    letter-spacing: 0.2em;
    text-transform: uppercase;
    color: var(--accent);
    flex-shrink: 0;
  }

  .step h2 {
    font-family: 'Fraunces', serif;
    font-weight: 400;
    font-size: clamp(28px, 4vw, 42px);
    line-height: 1.1;
    letter-spacing: -0.02em;
    font-variation-settings: 'opsz' 80;
  }

  .step h2 em {
    font-style: italic;
    color: var(--accent);
  }

  .step h3 {
    font-family: 'Fraunces', serif;
    font-style: italic;
    font-weight: 400;
    font-size: 22px;
    margin: 32px 0 14px;
    color: var(--ink);
  }

  .step p {
    margin-bottom: 16px;
    max-width: 68ch;
    color: var(--ink-soft);
  }

  .step p strong {
    color: var(--ink);
    font-weight: 500;
  }

  .step a.inline-link {
    color: var(--accent);
    text-decoration: underline;
    text-decoration-thickness: 1px;
    text-underline-offset: 3px;
  }

  .step ul, .step ol {
    margin: 12px 0 20px 24px;
    max-width: 66ch;
    color: var(--ink-soft);
  }

  .step ul li, .step ol li {
    margin-bottom: 6px;
  }

  .step code.inline {
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.88em;
    background: rgba(184, 65, 44, 0.08);
    color: var(--accent-deep);
    padding: 2px 6px;
    border-radius: 2px;
  }

  /* ===== Note callouts ===== */
  .note {
    background: var(--bg-card);
    border-left: 3px solid var(--accent);
    padding: 18px 22px;
    margin: 22px 0;
    font-family: 'Fraunces', serif;
    font-style: italic;
    font-size: 16px;
    color: var(--ink-soft);
  }

  .note strong {
    font-family: 'Inter Tight', sans-serif;
    font-style: normal;
    font-weight: 600;
    color: var(--accent);
    font-size: 11px;
    letter-spacing: 0.16em;
    text-transform: uppercase;
    display: block;
    margin-bottom: 6px;
  }

  .formula {
    background: var(--bg-card);
    border: 1px solid var(--rule);
    padding: 22px 24px;
    margin: 22px 0;
    text-align: center;
  }

  .formula .formula-label {
    font-family: 'JetBrains Mono', monospace;
    font-size: 10px;
    letter-spacing: 0.2em;
    text-transform: uppercase;
    color: var(--ink-muted);
    margin-bottom: 12px;
  }

  .formula .formula-math {
    font-family: 'Fraunces', serif;
    font-style: italic;
    font-size: 24px;
    color: var(--ink);
    letter-spacing: -0.01em;
  }

  .formula .formula-math .frac {
    display: inline-block;
    vertical-align: middle;
    text-align: center;
    margin: 0 6px;
  }

  .formula .formula-math .frac > span {
    display: block;
    padding: 2px 8px;
  }

  .formula .formula-math .frac > span:first-child {
    border-bottom: 1px solid var(--ink);
  }

  /* ===== Code Block ===== */
  .code-block {
    background: var(--code-bg);
    border: 1px solid var(--rule);
    margin: 20px 0 24px;
    overflow: hidden;
  }

  .code-tabs {
    display: flex;
    background: #15130F;
    border-bottom: 1px solid #2A2823;
  }

  .code-tab {
    background: transparent;
    border: none;
    color: #8C8578;
    padding: 10px 18px;
    font-family: 'JetBrains Mono', monospace;
    font-size: 11px;
    letter-spacing: 0.14em;
    text-transform: uppercase;
    cursor: pointer;
    border-right: 1px solid #2A2823;
    transition: background 0.15s, color 0.15s;
  }

  .code-tab:hover { color: #F4EFE6; }

  .code-tab.active {
    background: var(--code-bg);
    color: var(--accent);
  }

  .code-tab-spacer { flex: 1; border-right: 1px solid #2A2823; }

  .code-copy {
    background: transparent;
    border: none;
    color: #8C8578;
    padding: 10px 16px;
    font-family: 'JetBrains Mono', monospace;
    font-size: 10px;
    letter-spacing: 0.14em;
    text-transform: uppercase;
    cursor: pointer;
    transition: color 0.15s;
  }

  .code-copy:hover { color: var(--accent); }

  .code-panel {
    display: none;
    max-height: 540px;
    overflow: auto;
  }

  .code-panel.active { display: block; }

  pre {
    margin: 0;
    padding: 0;
  }

  pre code {
    font-family: 'JetBrains Mono', monospace;
    font-size: 12.5px;
    line-height: 1.65;
    padding: 20px 24px !important;
    display: block;
    background: var(--code-bg) !important;
  }

  /* Scrollbars inside code */
  .code-panel::-webkit-scrollbar { width: 10px; height: 10px; }
  .code-panel::-webkit-scrollbar-track { background: var(--code-bg); }
  .code-panel::-webkit-scrollbar-thumb { background: #3A3631; }
  .code-panel::-webkit-scrollbar-thumb:hover { background: var(--accent); }

  /* ===== Complete button ===== */
  .complete-btn {
    margin-top: 24px;
    background: transparent;
    border: 1px solid var(--rule);
    color: var(--ink);
    padding: 11px 22px;
    font-family: 'JetBrains Mono', monospace;
    font-size: 10px;
    letter-spacing: 0.18em;
    text-transform: uppercase;
    cursor: pointer;
    transition: all 0.2s;
    display: inline-flex;
    align-items: center;
    gap: 10px;
  }

  .complete-btn::before {
    content: '○';
    color: var(--ink-muted);
  }

  .complete-btn:hover {
    background: var(--ink);
    color: var(--bg);
  }

  .complete-btn.done {
    background: var(--accent);
    color: white;
    border-color: var(--accent);
  }

  .complete-btn.done::before {
    content: '✓';
    color: white;
  }

  /* ===== Colophon ===== */
  .colophon {
    margin-top: 64px;
    padding-top: 24px;
    border-top: 1px solid var(--rule);
    display: flex;
    justify-content: space-between;
    align-items: baseline;
    font-family: 'JetBrains Mono', monospace;
    font-size: 10px;
    letter-spacing: 0.14em;
    text-transform: uppercase;
    color: var(--ink-muted);
    flex-wrap: wrap;
    gap: 12px;
  }

  .colophon em {
    font-family: 'Fraunces', serif;
    font-style: italic;
    text-transform: none;
    letter-spacing: 0;
    font-size: 13px;
    color: var(--ink-soft);
  }

  @keyframes fadeUp {
    from { opacity: 0; transform: translateY(8px); }
    to { opacity: 1; transform: translateY(0); }
  }
  .title-block, .sidebar, .step { animation: fadeUp 0.5s ease-out both; }

  code.code-mono {
    font-family: 'JetBrains Mono', monospace;
    font-style: normal;
    font-size: 0.88em;
  }