/* ========= Base / tokens ========= */
:root {
  --bg: #0f1115;
  --bg-elev: #161922;
  --bg-side: #0b0d12;
  --fg: #e7e9ee;
  --fg-dim: #9aa3b2;
  --fg-mute: #6b7280;
  --accent: #7cc4ff;
  --accent-soft: #2a3a52;
  --rule: #232733;
  --code-bg: #11141b;
  --code-fg: #d8dee9;
  --kw: #c792ea;
  --str: #a3e635;
  --num: #f7c948;
  --com: #6b7280;
  --fn: #7cc4ff;
  --tip-bg: #15233a;
  --tip-bd: #2a4f8f;
  --warn-bg: #2a1a18;
  --warn-bd: #8a3a2c;
  --good-bg: #102a1f;
  --good-bd: #2c8a6a;
  --max-w: 760px;
}

@media (prefers-color-scheme: light) {
  :root.auto {
    --bg: #fafbfc;
    --bg-elev: #ffffff;
    --bg-side: #f3f4f7;
    --fg: #1f2330;
    --fg-dim: #4b5563;
    --fg-mute: #6b7280;
    --accent: #1e6fd9;
    --accent-soft: #d6e4f7;
    --rule: #e3e6ec;
    --code-bg: #f4f6fa;
    --code-fg: #1f2330;
    --kw: #7c3aed;
    --str: #166534;
    --num: #b45309;
    --com: #6b7280;
    --fn: #1e6fd9;
    --tip-bg: #e8f1fb;
    --tip-bd: #1e6fd9;
    --warn-bg: #fbeae5;
    --warn-bd: #c0392b;
    --good-bg: #e7f6ee;
    --good-bd: #1f8a55;
  }
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  background: var(--bg);
  color: var(--fg);
  font-family: 'Pretendard', -apple-system, BlinkMacSystemFont, 'Apple SD Gothic Neo', 'Noto Sans KR', sans-serif;
  font-size: 16px;
  line-height: 1.75;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }

/* ========= Index layout ========= */
.layout {
  display: grid;
  grid-template-columns: 320px 1fr;
  height: 100vh;
  overflow: hidden;
}

.sidebar {
  background: var(--bg-side);
  border-right: 1px solid var(--rule);
  overflow-y: auto;
  padding: 24px 20px 40px;
}

.sidebar .brand h1 {
  font-size: 18px;
  margin: 0 0 4px;
  letter-spacing: -0.01em;
  font-weight: 700;
}

.sidebar .brand p {
  margin: 0 0 24px;
  color: var(--fg-mute);
  font-size: 13px;
}

.sidebar .part-label {
  font-size: 11px;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  color: var(--fg-mute);
  margin: 18px 0 6px;
  padding: 0 8px;
  font-weight: 600;
}

.toc {
  list-style: none;
  margin: 0;
  padding: 0;
}

.toc li { margin: 0; }

.toc a {
  display: block;
  padding: 7px 10px;
  border-radius: 6px;
  color: var(--fg-dim);
  font-size: 14px;
  line-height: 1.45;
  transition: background 0.12s ease, color 0.12s ease;
}

.toc a:hover {
  background: var(--bg-elev);
  color: var(--fg);
  text-decoration: none;
}

.toc a.active {
  background: var(--accent-soft);
  color: var(--fg);
  font-weight: 500;
}

.toc .num {
  display: inline-block;
  width: 24px;
  color: var(--fg-mute);
  font-variant-numeric: tabular-nums;
  font-size: 12px;
}

.toc a.active .num { color: var(--accent); }

.main {
  background: var(--bg);
  overflow: hidden;
}

.main iframe {
  width: 100%;
  height: 100%;
  border: 0;
  background: var(--bg);
}

/* ========= Chapter page (inside iframe or standalone) ========= */
.chapter {
  max-width: var(--max-w);
  margin: 0 auto;
  padding: 56px 32px 120px;
}

.chapter .ch-head {
  border-bottom: 1px solid var(--rule);
  padding-bottom: 20px;
  margin-bottom: 32px;
}

.chapter .ch-num {
  font-size: 13px;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--accent);
  margin: 0 0 4px;
  font-weight: 600;
}

.chapter h1 {
  font-size: 30px;
  letter-spacing: -0.02em;
  margin: 0 0 8px;
  line-height: 1.25;
  font-weight: 700;
}

.chapter .subtitle {
  color: var(--fg-dim);
  font-size: 15px;
  margin: 0;
  line-height: 1.55;
}

.chapter h2 {
  font-size: 22px;
  letter-spacing: -0.01em;
  margin: 56px 0 16px;
  padding-top: 12px;
  font-weight: 700;
  border-top: 1px solid var(--rule);
  padding-top: 28px;
}

.chapter h2:first-of-type { border-top: 0; padding-top: 12px; }

.chapter h3 {
  font-size: 17px;
  margin: 32px 0 10px;
  font-weight: 600;
  color: var(--fg);
}

.chapter h4 {
  font-size: 15px;
  margin: 20px 0 8px;
  font-weight: 600;
  color: var(--fg-dim);
}

.chapter p {
  margin: 0 0 16px;
}

.chapter ul, .chapter ol {
  margin: 0 0 16px;
  padding-left: 24px;
}

.chapter li { margin: 4px 0; }

.chapter strong { color: var(--fg); font-weight: 600; }
.chapter em { color: var(--fg); font-style: italic; }

.chapter blockquote {
  margin: 16px 0;
  padding: 12px 16px;
  border-left: 3px solid var(--accent);
  background: var(--bg-elev);
  color: var(--fg-dim);
  border-radius: 0 6px 6px 0;
}

.chapter blockquote p:last-child { margin-bottom: 0; }

/* Inline code */
.chapter code {
  font-family: 'JetBrains Mono', 'Fira Code', ui-monospace, SFMono-Regular, monospace;
  font-size: 0.88em;
  background: var(--code-bg);
  color: var(--code-fg);
  padding: 1px 6px;
  border-radius: 4px;
  border: 1px solid var(--rule);
}

/* Code blocks */
.chapter pre {
  background: var(--code-bg);
  color: var(--code-fg);
  padding: 16px 18px;
  border-radius: 8px;
  border: 1px solid var(--rule);
  overflow-x: auto;
  font-family: 'JetBrains Mono', 'Fira Code', ui-monospace, SFMono-Regular, monospace;
  font-size: 13.5px;
  line-height: 1.6;
  margin: 0 0 18px;
}

.chapter pre code {
  background: transparent;
  border: 0;
  padding: 0;
  color: inherit;
  font-size: inherit;
}

/* Light syntax tinting via classes */
.chapter pre .kw { color: var(--kw); }
.chapter pre .str { color: var(--str); }
.chapter pre .num { color: var(--num); }
.chapter pre .com { color: var(--com); font-style: italic; }
.chapter pre .fn { color: var(--fn); }

/* Callouts */
.chapter .callout {
  margin: 18px 0;
  padding: 14px 16px 14px 18px;
  border-radius: 8px;
  border: 1px solid var(--rule);
  background: var(--bg-elev);
  font-size: 14.5px;
}

.chapter .callout .label {
  display: inline-block;
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  margin-bottom: 6px;
  color: var(--accent);
}

.chapter .callout.tip { background: var(--tip-bg); border-color: var(--tip-bd); }
.chapter .callout.tip .label { color: var(--accent); }
.chapter .callout.warn { background: var(--warn-bg); border-color: var(--warn-bd); }
.chapter .callout.warn .label { color: #f0846a; }
.chapter .callout.good { background: var(--good-bg); border-color: var(--good-bd); }
.chapter .callout.good .label { color: #6ee7b7; }

.chapter .callout p:last-child { margin-bottom: 0; }

/* ASCII figure */
.chapter .figure {
  margin: 18px 0;
  padding: 16px;
  background: var(--bg-elev);
  border: 1px solid var(--rule);
  border-radius: 8px;
  font-family: 'JetBrains Mono', ui-monospace, monospace;
  font-size: 12.5px;
  line-height: 1.5;
  white-space: pre;
  overflow-x: auto;
  color: var(--fg-dim);
}

.chapter .figure-caption {
  font-size: 13px;
  color: var(--fg-mute);
  text-align: center;
  margin-top: -8px;
  margin-bottom: 18px;
}

/* Tables */
.chapter table {
  width: 100%;
  border-collapse: collapse;
  margin: 16px 0;
  font-size: 14px;
}

.chapter th, .chapter td {
  text-align: left;
  padding: 8px 12px;
  border-bottom: 1px solid var(--rule);
}

.chapter th {
  background: var(--bg-elev);
  font-weight: 600;
}

/* Footer nav inside chapter */
.chapter-nav {
  display: flex;
  justify-content: space-between;
  margin-top: 64px;
  padding-top: 24px;
  border-top: 1px solid var(--rule);
  gap: 16px;
}

.chapter-nav a {
  flex: 1;
  padding: 14px 18px;
  background: var(--bg-elev);
  border: 1px solid var(--rule);
  border-radius: 8px;
  display: flex;
  flex-direction: column;
  font-size: 13px;
  color: var(--fg-dim);
}

.chapter-nav a:hover {
  background: var(--accent-soft);
  border-color: var(--accent);
  text-decoration: none;
  color: var(--fg);
}

.chapter-nav .dir {
  font-size: 11px;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--fg-mute);
  margin-bottom: 4px;
}

.chapter-nav .next { text-align: right; align-items: flex-end; }

/* Recap box at end of chapter */
.chapter .recap {
  margin-top: 32px;
  padding: 20px 22px;
  background: var(--bg-elev);
  border: 1px solid var(--rule);
  border-radius: 10px;
}

.chapter .recap h3 {
  margin-top: 0;
  font-size: 15px;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  color: var(--accent);
}

.chapter .recap ul {
  margin: 8px 0 0;
  padding-left: 22px;
}

.chapter .recap li {
  margin: 6px 0;
  color: var(--fg-dim);
}

/* Responsive */
@media (max-width: 900px) {
  .layout { grid-template-columns: 1fr; height: auto; overflow: auto; }
  .sidebar { height: auto; max-height: 50vh; border-right: 0; border-bottom: 1px solid var(--rule); }
  .main { height: 70vh; }
  .chapter { padding: 40px 20px 80px; }
}

/* Home page (intro card on iframe before any chapter) */
.home {
  max-width: var(--max-w);
  margin: 0 auto;
  padding: 80px 32px;
}

.home h1 {
  font-size: 34px;
  letter-spacing: -0.02em;
  margin: 0 0 6px;
  line-height: 1.2;
}

.home .lede {
  color: var(--fg-dim);
  font-size: 16px;
  margin: 0 0 28px;
  line-height: 1.6;
}

.home .meta {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  gap: 12px;
  margin: 32px 0;
}

.home .meta .card {
  background: var(--bg-elev);
  border: 1px solid var(--rule);
  border-radius: 8px;
  padding: 14px 16px;
}

.home .meta .card .k {
  font-size: 11px;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--fg-mute);
  margin-bottom: 4px;
}

.home .meta .card .v { font-size: 16px; font-weight: 600; }