:root {
  --brand: #F4651B;
  --brand-strong: #C2410C;
  --brand-soft: #FFF1E8;
  --info: #185FA5;
  --info-soft: #E6F1FB;
  --gold: #854F0B;
  --gold-soft: #FAEEDA;
  --gray-soft: #F1EFE8;

  /* light theme surfaces */
  --bg: #FFFFFF;
  --bg-2: #FAFAF8;
  --bg-3: #F1EFE8;
  --text: #1F1E1B;
  --text-2: #5F5E5A;
  --text-3: #9A988F;
  --border: #E6E3DB;
  --border-2: #D6D3CA;
  --shadow: 0 1px 2px rgba(0,0,0,.04), 0 4px 16px rgba(0,0,0,.05);
  --code-bg: #F6F5F1;

  --content-w: 720px;
  --sidebar-w: 248px;
  --rail-w: 200px;
  --radius: 12px;
  --radius-sm: 8px;
  --font: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "Source Han Sans SC", sans-serif;
  --mono: "SFMono-Regular", "JetBrains Mono", Consolas, "Liberation Mono", Menlo, monospace;
}

[data-theme="dark"] {
  --brand: #FF8A4C;
  --brand-strong: #FF8A4C;
  --brand-soft: #3a2417;
  --info: #7FB6EF;
  --info-soft: #16283b;
  --gold: #E7B873;
  --gold-soft: #362a17;
  --gray-soft: #232220;

  --bg: #16150F;
  --bg-2: #1E1D18;
  --bg-3: #26241E;
  --text: #ECE9E2;
  --text-2: #B7B3A8;
  --text-3: #807C72;
  --border: #322F28;
  --border-2: #403C33;
  --shadow: 0 1px 2px rgba(0,0,0,.3), 0 6px 20px rgba(0,0,0,.35);
  --code-bg: #211F19;
}

* { box-sizing: border-box; }
[hidden] { display: none !important; }
html { scroll-behavior: smooth; background: var(--bg); }
body {
  margin: 0;
  font-family: var(--font);
  background: var(--bg-2);
  color: var(--text);
  font-size: 17px;
  line-height: 1.8;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}
a { color: var(--brand-strong); text-decoration: none; }
a:hover { text-decoration: underline; }

/* ---------- progress bar ---------- */
#progress {
  position: fixed; top: 0; left: 0; height: 3px; width: 0%;
  background: var(--brand); z-index: 60; transition: width .1s linear;
}

/* ---------- top bar ---------- */
.topbar {
  position: sticky; top: 0; z-index: 50;
  display: flex; align-items: center; gap: 12px;
  height: 56px; padding: 0 16px;
  background: var(--bg); border-bottom: 1px solid var(--border);
}
.brand { display: flex; align-items: center; gap: 10px; font-weight: 600; color: var(--text); min-width: 0; }
.brand:hover { text-decoration: none; }
.brand .logo { width: 22px; height: 22px; border-radius: 6px; background: var(--brand); flex: none; }
.brand-text { white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
.topbar-actions { margin-left: auto; display: flex; align-items: center; gap: 8px; }
.icon-btn {
  height: 38px; min-width: 38px; padding: 0 10px; border-radius: 10px;
  border: 1px solid var(--border); background: var(--bg); color: var(--text-2);
  font-size: 15px; cursor: pointer; display: inline-flex; align-items: center; justify-content: center;
}
.icon-btn:hover { color: var(--brand); border-color: var(--brand); }
.menu-btn { display: none; }

/* search */
.search-box { position: relative; }
.search-box input {
  height: 38px; width: 200px; max-width: 42vw; padding: 0 12px; border-radius: 10px;
  border: 1px solid var(--border); background: var(--bg-2); color: var(--text); font-size: 14px;
}
.search-box input:focus { outline: none; border-color: var(--brand); width: 240px; }
.search-results {
  position: absolute; top: 44px; right: 0; width: min(420px, 86vw);
  max-height: 60vh; overflow-y: auto; background: var(--bg); border: 1px solid var(--border);
  border-radius: var(--radius); box-shadow: var(--shadow); padding: 6px; z-index: 55;
}
.search-results .sr-item { display: block; padding: 8px 10px; border-radius: 8px; color: var(--text); }
.search-results .sr-item:hover, .search-results .sr-item.active { background: var(--brand-soft); text-decoration: none; }
.search-results .sr-title { font-weight: 600; font-size: 14px; }
.search-results .sr-snippet { font-size: 12px; color: var(--text-2); margin-top: 2px; line-height: 1.5; }
.search-results .sr-snippet mark { background: #FFE08A; color: #3a2c00; border-radius: 3px; padding: 0 2px; }
.search-results .sr-empty { padding: 12px; color: var(--text-3); font-size: 13px; }

/* ---------- layout ---------- */
.layout {
  display: grid;
  grid-template-columns: var(--sidebar-w) minmax(0, 1fr) var(--rail-w);
  gap: 0; max-width: 1400px; margin: 0 auto;
}
.sidebar {
  position: sticky; top: 56px; align-self: start;
  height: calc(100vh - 56px); overflow-y: auto; padding: 18px 12px 40px;
  border-right: 1px solid var(--border); background: var(--bg);
}
.content { padding: 28px 32px 80px; min-width: 0; }
.rail {
  position: sticky; top: 56px; align-self: start;
  height: calc(100vh - 56px); overflow-y: auto; padding: 24px 14px;
  border-left: 1px solid var(--border); background: var(--bg);
}

/* ---------- sidebar TOC ---------- */
.toc-part { margin-bottom: 6px; }
.toc-part > summary {
  cursor: pointer; font-weight: 600; font-size: 13px; color: var(--text-2);
  padding: 8px 8px; border-radius: 8px; list-style: none; user-select: none;
}
.toc-part > summary::-webkit-details-marker { display: none; }
.toc-part > summary::before { content: "▸"; display: inline-block; margin-right: 6px; transition: transform .15s; color: var(--text-3); }
.toc-part[open] > summary::before { transform: rotate(90deg); }
.toc-children { padding-left: 10px; border-left: 1px solid var(--border); margin-left: 10px; }
.toc-item { margin: 1px 0; }
.toc-link {
  display: block; padding: 6px 10px; border-radius: 8px; color: var(--text-2);
  font-size: 14px; line-height: 1.45; border-left: 3px solid transparent;
}
.toc-link:hover { background: var(--bg-2); color: var(--text); text-decoration: none; }
.toc-link.lv1 { font-weight: 600; color: var(--text); }
.toc-link.lv2 { font-size: 13px; padding-left: 14px; }
.toc-link.lv3 { font-size: 12.5px; padding-left: 22px; color: var(--text-3); }
.toc-link.active {
  background: var(--brand-soft); color: var(--brand-strong); border-left-color: var(--brand); font-weight: 600;
}

/* ---------- article ---------- */
.book { max-width: var(--content-w); margin: 0 auto; font-size: var(--book-fs, 17px); }
.book h1, .book h2, .book h3, .book h4 { scroll-margin-top: 72px; line-height: 1.35; }
.book h1 { font-size: 28px; margin: 8px 0 18px; }
.book h2 { font-size: 22px; margin: 34px 0 14px; padding-bottom: 8px; border-bottom: 1px solid var(--border); }
.book h3 { font-size: 18px; margin: 26px 0 10px; }
.book h4 { font-size: 16px; margin: 20px 0 8px; color: var(--text); }
.book p { margin: 14px 0; }
.book ul, .book ol { padding-left: 1.5em; margin: 14px 0; }
.book li { margin: 6px 0; }
.book img.book-img { max-width: 100%; height: auto; border-radius: var(--radius); display: block; margin: 8px auto 24px; border: 1px solid var(--border-2); cursor: zoom-in; box-shadow: 0 4px 24px rgba(0,0,0,.08); }
/* 封面图上方区域：干净的标题展示 */
.book > p:first-child { margin: 0 auto 4px; text-align: center; }
.book strong { color: var(--text); }
.book code {
  font-family: var(--mono); font-size: .88em; background: var(--code-bg);
  padding: .12em .4em; border-radius: 5px; border: 1px solid var(--border);
}
.book pre {
  position: relative; background: var(--code-bg); border: 1px solid var(--border);
  border-radius: var(--radius); padding: 14px 14px; overflow-x: auto; margin: 18px 0;
}
.book pre code { background: none; border: none; padding: 0; font-size: 13.5px; line-height: 1.6; }
.copy-btn {
  position: absolute; top: 8px; right: 8px; font-size: 12px; padding: 4px 9px;
  border: 1px solid var(--border); border-radius: 7px; background: var(--bg); color: var(--text-2); cursor: pointer;
}
.copy-btn:hover { color: var(--brand); border-color: var(--brand); }

/* tables */
.table-wrap { overflow-x: auto; margin: 18px 0; border: 1px solid var(--border); border-radius: var(--radius); }
.book table { border-collapse: collapse; width: 100%; font-size: 14px; }
.book th, .book td { border-bottom: 1px solid var(--border); padding: 9px 12px; text-align: left; }
.book th { background: var(--bg-3); font-weight: 600; }
.book tr:last-child td { border-bottom: none; }

/* blockquote */
.book blockquote { margin: 18px 0; padding: 12px 16px; border-left: 4px solid var(--border-2); background: var(--bg-2); border-radius: 0 var(--radius-sm) var(--radius-sm) 0; color: var(--text-2); }
.book blockquote p { margin: 6px 0; }
.book blockquote.quote { font-style: italic; }

/* callout: 功能快照 */
.book blockquote.callout-info {
  border-left: 4px solid var(--info); background: var(--info-soft); color: var(--text); font-style: normal;
}
.book blockquote.callout-info p:first-child strong { color: var(--info); display: block; margin-bottom: 4px; }
.book p.callout-info {
  border-left: 4px solid var(--info); background: var(--info-soft); color: var(--text); font-style: normal;
  padding: 12px 16px; border-radius: 0 var(--radius-sm) var(--radius-sm) 0; margin: 16px 0;
}
.book p.callout-info strong:first-child { color: var(--info); }

/* fixed sections */
.block-recap { margin: 22px 0; padding: 16px 18px; background: var(--gray-soft); border-left: 4px solid var(--text-3); border-radius: 0 var(--radius) var(--radius) 0; }
.block-golden { margin: 22px 0; padding: 16px 18px; background: var(--gold-soft); border-left: 4px solid var(--gold); border-radius: 0 var(--radius) var(--radius) 0; }
.block-golden h2 { border: none; color: var(--gold); margin-top: 0; }
.block-tryit { margin: 22px 0; padding: 16px 18px; background: var(--brand-soft); border-left: 4px solid var(--brand); border-radius: 0 var(--radius) var(--radius) 0; }
.block-tryit h2 { border: none; color: var(--brand-strong); margin-top: 0; }
.block-recap h2, .block-golden h2, .block-tryit h2 { font-size: 19px; }
.book .block-recap h2 { color: var(--text-2); }

/* ---------- pager ---------- */
.pager { max-width: var(--content-w); margin: 48px auto 0; display: flex; gap: 12px; }
.pager a {
  flex: 1; padding: 14px 16px; border: 1px solid var(--border); border-radius: var(--radius);
  color: var(--text); background: var(--bg); font-size: 14px;
}
.pager a:hover { border-color: var(--brand); color: var(--brand-strong); text-decoration: none; }
.pager .pager-prev::before { content: "← "; color: var(--text-3); }
.pager .pager-next { text-align: right; }
.pager .pager-next::after { content: " →"; color: var(--text-3); }
.pager a.disabled { visibility: hidden; }

/* ---------- right rail ---------- */
.rail-title { font-size: 12px; font-weight: 600; color: var(--text-3); text-transform: uppercase; letter-spacing: .04em; margin-bottom: 10px; }
.rail-link { display: block; padding: 5px 10px; font-size: 13px; color: var(--text-2); border-left: 2px solid var(--border); border-radius: 0 6px 6px 0; margin: 2px 0; line-height: 1.4; }
.rail-link:hover { color: var(--text); text-decoration: none; background: var(--bg-2); }
.rail-link.lv3 { padding-left: 20px; font-size: 12.5px; color: var(--text-3); }
.rail-link.active { color: var(--brand-strong); border-left-color: var(--brand); background: var(--brand-soft); font-weight: 600; }

/* ---------- back to top ---------- */
.back-top {
  position: fixed; right: 22px; bottom: 22px; width: 44px; height: 44px; border-radius: 50%;
  border: 1px solid var(--border); background: var(--bg); color: var(--brand); font-size: 20px; cursor: pointer;
  box-shadow: var(--shadow); z-index: 45;
}

/* ---------- drawer overlay (mobile) ---------- */
.drawer-overlay {
  position: fixed; inset: 0; background: rgba(0,0,0,.4); z-index: 70;
  display: none; justify-content: flex-end;
}
.drawer-overlay:not([hidden]) { display: flex; }
.drawer-overlay .sidebar {
  position: relative; top: 0; height: 100%; width: 82vw; max-width: 320px;
  animation: slidein .2s ease; box-shadow: var(--shadow);
}
@keyframes slidein { from { transform: translateX(20px); opacity: .6; } to { transform: none; opacity: 1; } }

/* ---------- lightbox ---------- */
.lightbox { position: fixed; inset: 0; background: rgba(0,0,0,.86); z-index: 80; display: none; align-items: center; justify-content: center; padding: 24px; }
.lightbox:not([hidden]) { display: flex; }
.lightbox img { max-width: 94vw; max-height: 90vh; border-radius: var(--radius); box-shadow: 0 10px 40px rgba(0,0,0,.5); }
.lightbox-close { position: absolute; top: 16px; right: 20px; width: 40px; height: 40px; border-radius: 50%; border: none; background: rgba(255,255,255,.15); color: #fff; font-size: 22px; cursor: pointer; }

/* ---------- responsive ---------- */
@media (max-width: 1100px) {
  .layout { grid-template-columns: var(--sidebar-w) minmax(0, 1fr); }
  .rail { display: none; }
}
@media (max-width: 768px) {
  body { font-size: 16px; }
  .menu-btn { display: inline-flex; }
  .layout { grid-template-columns: minmax(0, 1fr); }
  .sidebar { display: none; }
  .sidebar.open { display: block; }
  .content { padding: 18px 16px 90px; }
  .brand-text { display: none; }
  .search-box input { width: 140px; }
  .search-box input:focus { width: 170px; }
  .book h1 { font-size: 24px; }
  .book h2 { font-size: 20px; }
  .topbar { gap: 8px; padding: 0 10px; }
  .drawer-overlay .sidebar { padding-top: 18px; }
  .pager { position: fixed; left: 0; right: 0; bottom: 0; margin: 0; display: flex; z-index: 40; background: var(--bg); border-top: 1px solid var(--border); padding: 8px; gap: 8px; }
  .pager a { border-radius: 10px; padding: 12px; }
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  * { animation: none !important; transition: none !important; }
}