:root {
  --bg: #f7f7f5;
  --surface: #ffffff;
  --sidebar-bg: #1f2530;
  --sidebar-fg: #c7cdd6;
  --sidebar-muted: #8b95a5;
  --sidebar-active: #2dd4bf;
  --text: #24292f;
  --text-soft: #57606a;
  --border: #e3e3df;
  --accent: #0f766e;
  --accent-soft: #ccfbf1;
  --code-bg: #f2f1ee;
  --max-read: 820px;
  --sidebar-w: 300px;
  --toc-w: 240px;
  --mono: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, "Liberation Mono", monospace;
  --sans: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Hiragino Sans GB",
    "Microsoft YaHei", "Noto Sans CJK SC", "Source Han Sans SC", sans-serif;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  font-family: var(--sans);
  background: var(--bg);
  color: var(--text);
  line-height: 1.75;
  font-size: 16.5px;
  -webkit-font-smoothing: antialiased;
}

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

/* ----------------------------- Sidebar ----------------------------- */
.sidebar {
  position: fixed;
  top: 0;
  left: 0;
  width: var(--sidebar-w);
  height: 100vh;
  background: var(--sidebar-bg);
  color: var(--sidebar-fg);
  overflow-y: auto;
  padding: 0 0 40px;
  z-index: 40;
  scrollbar-width: thin;
  scrollbar-color: #3a4252 transparent;
}
.sidebar::-webkit-scrollbar { width: 8px; }
.sidebar::-webkit-scrollbar-thumb { background: #3a4252; border-radius: 4px; }

.brand {
  display: block;
  padding: 22px 22px 16px;
  border-bottom: 1px solid #2c333f;
  position: sticky;
  top: 0;
  background: var(--sidebar-bg);
  z-index: 2;
}
.brand:hover { text-decoration: none; }
.brand-title {
  display: block;
  font-size: 18px;
  font-weight: 700;
  color: #fff;
  letter-spacing: .3px;
}
.brand-sub {
  display: block;
  font-size: 12px;
  color: var(--sidebar-muted);
  margin-top: 4px;
}

.nav-search { padding: 14px 18px 6px; }
.nav-search input {
  width: 100%;
  background: #161b22;
  border: 1px solid #2c333f;
  color: #e6e9ee;
  border-radius: 8px;
  padding: 8px 12px;
  font-size: 13.5px;
  outline: none;
}
.nav-search input:focus { border-color: var(--sidebar-active); }

.nav-section { padding: 8px 0 4px; }
.nav-section-title {
  font-size: 11.5px;
  text-transform: uppercase;
  letter-spacing: 1.4px;
  color: var(--sidebar-muted);
  margin: 14px 0 6px;
  padding: 0 22px;
}
.sidebar ul { list-style: none; margin: 0; padding: 0; }
.sidebar li a {
  display: flex;
  align-items: baseline;
  gap: 8px;
  padding: 7px 22px;
  color: var(--sidebar-fg);
  font-size: 14px;
  border-left: 3px solid transparent;
  transition: background .12s, color .12s;
}
.sidebar li a:hover { background: #262d39; text-decoration: none; color: #fff; }
.sidebar li.active a {
  background: #262d39;
  border-left-color: var(--sidebar-active);
  color: #fff;
}
.nav-tag {
  flex: 0 0 auto;
  font-size: 11px;
  color: var(--sidebar-muted);
  font-variant-numeric: tabular-nums;
  min-width: 44px;
}
.sidebar li.active .nav-tag { color: var(--sidebar-active); }
.nav-name { flex: 1; }

/* ----------------------------- Content ----------------------------- */
.content {
  margin-left: var(--sidebar-w);
  padding: 48px 56px 96px;
  display: flex;
  gap: 40px;
  justify-content: center;
  align-items: flex-start;
  min-width: 0;
}
.note {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 48px 56px 40px;
  max-width: var(--max-read);
  width: 100%;
  min-width: 0;
  box-shadow: 0 1px 2px rgba(0,0,0,.04);
}

.note h1 {
  font-size: 30px;
  line-height: 1.35;
  margin: 0 0 24px;
  padding-bottom: 18px;
  border-bottom: 2px solid var(--border);
  font-weight: 700;
}
.note h2 {
  font-size: 23px;
  margin: 44px 0 16px;
  padding-left: 12px;
  border-left: 4px solid var(--accent);
  font-weight: 700;
  scroll-margin-top: 24px;
}
.note h3 {
  font-size: 19px;
  margin: 32px 0 12px;
  font-weight: 700;
  color: #1b1f24;
  scroll-margin-top: 24px;
}
.note h4 { font-size: 16.5px; margin: 24px 0 10px; font-weight: 700; }

.note p { margin: 14px 0; }
.note ul, .note ol { padding-left: 26px; margin: 14px 0; }
.note li { margin: 6px 0; }
.note li > ul, .note li > ol { margin: 6px 0; }
.note h1,
.note h2,
.note h3,
.note h4,
.note p,
.note li,
.note blockquote {
  overflow-wrap: anywhere;
}

.note strong { font-weight: 700; color: #1b1f24; }
.note hr { border: none; border-top: 1px solid var(--border); margin: 36px 0; }

/* Plain blockquotes (e.g. chapter epigraphs). */
.note blockquote {
  margin: 18px 0;
  padding: 4px 20px;
  border-left: 4px solid #d0d7de;
  color: var(--text-soft);
  font-style: italic;
  background: #fbfbfa;
  border-radius: 0 8px 8px 0;
}
.note blockquote p { margin: 8px 0; }

/* Inline + block code. */
.note code {
  font-family: var(--mono);
  background: var(--code-bg);
  padding: 2px 6px;
  border-radius: 5px;
  font-size: .9em;
}
.note pre {
  background: #1f2530;
  color: #e6e9ee;
  padding: 16px 18px;
  border-radius: 10px;
  overflow-x: auto;
  font-size: 13.5px;
  line-height: 1.6;
}
.note pre code { background: none; padding: 0; color: inherit; font-size: inherit; }

/* Images. */
.note img {
  display: block;
  max-width: 100%;
  height: auto;
  margin: 22px auto;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: #fff;
  padding: 6px;
}

/* Tables. */
.note table {
  border-collapse: collapse;
  width: 100%;
  margin: 22px 0;
  font-size: 14.5px;
  display: block;
  overflow-x: auto;
}
.note th, .note td {
  border: 1px solid var(--border);
  padding: 9px 13px;
  text-align: left;
  vertical-align: top;
}
.note thead th { background: #f1f3f2; font-weight: 700; }
.note tbody tr:nth-child(even) { background: #fafafa; }

/* Math. */
.math-display {
  margin: 20px 0;
  overflow-x: auto;
  overflow-y: hidden;
  padding: 4px 0;
  text-align: center;
}
.katex { font-size: 1.05em; }
.math-error { color: #b91c1c; background: #fee2e2; }

/* ----------------------------- Callouts ---------------------------- */
.callout {
  margin: 20px 0;
  border-radius: 10px;
  border: 1px solid var(--border);
  border-left-width: 4px;
  background: var(--surface);
  overflow: hidden;
}
.callout-title {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 10px 16px;
  font-weight: 700;
  font-size: 14.5px;
}
.callout-icon { font-size: 15px; }
.callout-body { padding: 2px 16px 12px; }
.callout-body > :first-child { margin-top: 4px; }
.callout-body > :last-child { margin-bottom: 4px; }

.callout-note { border-left-color: #6b7280; }
.callout-note .callout-title { background: #f3f4f6; color: #374151; }
.callout-info { border-left-color: #0ea5e9; }
.callout-info .callout-title { background: #e0f2fe; color: #075985; }
.callout-tip { border-left-color: #10b981; }
.callout-tip .callout-title { background: #d1fae5; color: #065f46; }
.callout-important { border-left-color: #0f766e; }
.callout-important .callout-title { background: var(--accent-soft); color: #115e59; }
.callout-warning { border-left-color: #f59e0b; }
.callout-warning .callout-title { background: #fef3c7; color: #92400e; }
.callout-danger { border-left-color: #ef4444; }
.callout-danger .callout-title { background: #fee2e2; color: #991b1b; }

/* ----------------------------- Pager ------------------------------- */
.pager-row {
  display: flex;
  gap: 16px;
  margin-top: 48px;
  padding-top: 24px;
  border-top: 1px solid var(--border);
}
.pager {
  flex: 1 1 0;
  display: flex;
  flex-direction: column;
  gap: 4px;
  padding: 14px 18px;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: #fbfbfa;
  min-width: 0;
}
.pager:hover { border-color: var(--accent); text-decoration: none; background: #fff; }
.pager.next { text-align: right; }
.pager.placeholder { background: none; border: none; }
.pager-dir { font-size: 12px; color: var(--text-soft); }
.pager-name { font-weight: 600; color: var(--text); overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }

/* ------------------------------- TOC ------------------------------- */
.toc {
  position: sticky;
  top: 32px;
  flex: 0 0 var(--toc-w);
  width: var(--toc-w);
  max-height: calc(100vh - 64px);
  overflow-y: auto;
  font-size: 13.5px;
  padding-left: 4px;
}
.toc-title {
  font-weight: 700;
  font-size: 12px;
  text-transform: uppercase;
  letter-spacing: 1px;
  color: var(--text-soft);
  margin-bottom: 10px;
}
.toc ul { list-style: none; margin: 0; padding: 0; border-left: 1px solid var(--border); }
.toc li a {
  display: block;
  padding: 4px 12px;
  color: var(--text-soft);
  border-left: 2px solid transparent;
  margin-left: -1px;
  line-height: 1.5;
}
.toc li a:hover { color: var(--accent); text-decoration: none; }
.toc li a.active { color: var(--accent); border-left-color: var(--accent); font-weight: 600; }
.toc-l3 a { padding-left: 24px; font-size: 12.5px; }

/* ----------------------------- Mobile ------------------------------ */
.menu-toggle {
  display: none;
  position: fixed;
  top: 12px;
  left: 12px;
  z-index: 60;
  width: 42px;
  height: 42px;
  border: none;
  border-radius: 10px;
  background: var(--sidebar-bg);
  color: #fff;
  font-size: 20px;
  cursor: pointer;
  box-shadow: 0 2px 8px rgba(0,0,0,.2);
}
.overlay {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,.45);
  z-index: 35;
}

@media (max-width: 1180px) {
  .toc { display: none; }
  .content { padding: 48px 32px 96px; }
}
@media (max-width: 860px) {
  .menu-toggle { display: block; }
  .sidebar {
    transform: translateX(-100%);
    transition: transform .25s ease;
    box-shadow: 2px 0 16px rgba(0,0,0,.3);
  }
  body.nav-open .sidebar { transform: translateX(0); }
  body.nav-open .overlay { display: block; }
  .content { margin-left: 0; padding: 64px 16px 80px; }
  .note { padding: 28px 20px 28px; border-radius: 10px; }
  .note h1 { font-size: 24px; overflow-wrap: anywhere; }
  .note h2 { font-size: 20px; }
  .pager-row { flex-direction: column; }
}

/* ------------------------------ Home ------------------------------- */
body.home { background: var(--bg); }
.hero {
  text-align: center;
  padding: 72px 24px 40px;
  max-width: 900px;
  margin: 0 auto;
}
.hero h1 { font-size: 38px; margin: 0 0 12px; font-weight: 800; letter-spacing: .5px; }
.hero-sub { font-size: 17px; color: var(--accent); font-weight: 600; margin: 0 0 18px; }
.hero-desc { font-size: 15.5px; color: var(--text-soft); line-height: 1.8; max-width: 680px; margin: 0 auto; }

.home-main { max-width: 1080px; margin: 0 auto; padding: 0 24px 80px; }
.home-section-title {
  font-size: 20px;
  margin: 40px 0 18px;
  padding-bottom: 10px;
  border-bottom: 2px solid var(--border);
}
.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(240px, 1fr));
  gap: 14px;
}
.card {
  display: flex;
  flex-direction: column;
  gap: 5px;
  padding: 16px 18px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 12px;
  transition: transform .12s, box-shadow .12s, border-color .12s;
}
.card:hover {
  text-decoration: none;
  transform: translateY(-2px);
  box-shadow: 0 6px 18px rgba(0,0,0,.08);
  border-color: var(--accent);
}
.card-tag { font-size: 12px; color: var(--accent); font-weight: 700; letter-spacing: .5px; }
.card-name { font-size: 15.5px; font-weight: 600; color: var(--text); line-height: 1.5; }
.card-en { font-size: 12px; color: var(--text-soft); line-height: 1.4; }
.home-footer {
  text-align: center;
  color: var(--text-soft);
  font-size: 13px;
  padding: 30px 24px 60px;
}

@media (max-width: 520px) {
  .hero { padding: 56px 24px 34px; }
  .hero h1 {
    font-size: 34px;
    line-height: 1.28;
    overflow-wrap: anywhere;
  }
  .hero-desc { font-size: 15px; }
  .card-grid { grid-template-columns: 1fr; }
}