/* ==================================================================
   优化理论 · 逐页精讲 —— 全站样式
   字体：Times New Roman（西文）+ 宋体（中文）；例子框用楷体。
   公式：KaTeX 在构建时排好，这里只管字号与溢出。
   流畅度：不用 backdrop-filter、不用大面积阴影和滚动动画；
           页面只有一个主滚动条（目录栏有自己的滚动）。
   ================================================================== */

:root {
  --font-scale: 1;
  --font-body: "Times New Roman", Times, "Nimbus Roman", "TeX Gyre Termes", "Liberation Serif",
    "Songti SC", "STSong", "SimSun", "宋体", "Noto Serif CJK SC", "Source Han Serif SC", serif;
  --font-kai: "Times New Roman", Times, "Nimbus Roman", "Kaiti SC", "STKaiti", "KaiTi", "楷体",
    "LXGW WenKai", "Noto Serif CJK SC", serif;
  --font-mono: ui-monospace, SFMono-Regular, Menlo, Consolas, "Liberation Mono", monospace;

  --bg: #f6f4ef;
  --paper: #ffffff;
  --ink: #1d2433;
  --ink-2: #4a5263;
  --muted: #8a90a0;
  --line: #e3dfd6;
  --line-2: #d4cec2;
  --accent: #1f4e8c;
  --accent-2: #b5452f;
  --accent-soft: #e8eff9;

  --navy: #1f4e8c;
  --blue: #3b73c4;
  --red: #c0392b;
  --teal: #0f7b6c;
  --orange: #d97706;
  --purple: #6d28d9;
  --green: #2f7d32;
  --gray: #6b7280;
  --fill-blue: #dbe7f6;
  --fill-red: #f8dcd8;
  --fill-teal: #d5efe9;
  --fill-orange: #fdecd3;
  --fill-gray: #eceae4;
  --fill-purple: #ebe4fb;

  --topbar-h: 56px;
  --nav-w: 272px;
  --radius: 10px;
}

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

html {
  font-size: calc(17px * var(--font-scale));
  -webkit-text-size-adjust: 100%;
  scroll-padding-top: calc(var(--topbar-h) + 14px);
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: var(--font-body);
  line-height: 1.9;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

img { max-width: 100%; }
a { color: var(--accent); text-decoration-thickness: 1px; text-underline-offset: 0.2em; }
a:hover { color: #163a6a; }
button { font: inherit; color: inherit; }
kbd {
  display: inline-block; min-width: 1.6em; padding: 0 0.4em; font-family: var(--font-body);
  font-size: 0.78em; line-height: 1.5; text-align: center; color: var(--ink-2);
  background: #fff; border: 1px solid var(--line-2); border-bottom-width: 2px; border-radius: 5px;
}
:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }

.skip-link { position: absolute; left: -9999px; top: 8px; z-index: 200; background: #fff; padding: 6px 12px; border-radius: 6px; }
.skip-link:focus { left: 12px; }

/* ------------------------------------------------------------------ */
/* 顶栏                                                                */
/* ------------------------------------------------------------------ */

.topbar {
  position: sticky; top: 0; z-index: 50;
  height: var(--topbar-h);
  background: #fff;
  border-bottom: 1px solid var(--line);
}
.topbar-inner {
  height: 100%; display: flex; align-items: center; gap: 14px;
  padding: 0 18px;
}
.brand {
  flex: none; color: var(--ink); text-decoration: none; white-space: nowrap;
  font-size: 1.06rem; font-weight: 700; letter-spacing: 0.02em;
}
.brand span { margin-left: 0.45em; color: var(--accent); font-weight: 400; }
.crumbs {
  flex: 1 1 auto; min-width: 0; display: flex; align-items: center; gap: 6px;
  overflow: hidden; white-space: nowrap; font-size: 0.86rem; color: var(--ink-2);
}
.crumbs a { color: var(--ink-2); text-decoration: none; }
.crumbs a:hover { color: var(--accent); }
.crumbs > :last-child { overflow: hidden; text-overflow: ellipsis; }
.crumb-sep { color: var(--muted); }
.crumb-live:empty { display: none; }
.crumbs .crumb-sep:has(+ .crumb-live:empty) { display: none; }
.tools { flex: none; display: flex; align-items: center; gap: 8px; }
.font-tools { display: flex; gap: 4px; }

.tool-btn, .icon-btn {
  display: inline-flex; align-items: center; justify-content: center; gap: 6px;
  height: 34px; padding: 0 10px; border-radius: 8px; cursor: pointer;
  background: #fff; border: 1px solid var(--line); color: var(--ink-2);
  font-size: 0.86rem; line-height: 1; white-space: nowrap;
}
.tool-btn:hover, .icon-btn:hover { border-color: var(--accent); color: var(--accent); }
.tool-btn svg, .icon-btn svg, .lb-btn svg, .search-input-row svg, .zoom-hint svg {
  width: 17px; height: 17px; fill: none; stroke: currentColor; stroke-width: 1.8;
  stroke-linecap: round; stroke-linejoin: round;
}
.nav-toggle { display: none; width: 38px; padding: 0; }

.read-progress { position: absolute; left: 0; right: 0; bottom: -1px; height: 2px; pointer-events: none; }
.read-progress span {
  display: block; height: 100%; background: var(--accent-2);
  transform-origin: 0 50%; transform: scaleX(0);
}

@media (max-width: 1199px) {
  .nav-toggle { display: inline-flex; }
}
@media (max-width: 760px) {
  .topbar-inner { gap: 8px; padding: 0 10px; }
  .brand span, .search-open span, .search-open kbd { display: none; }
  .crumbs { display: none; }
  .tools { margin-left: auto; }
}

/* ------------------------------------------------------------------ */
/* 布局与目录栏                                                         */
/* ------------------------------------------------------------------ */

.layout { display: grid; grid-template-columns: var(--nav-w) minmax(0, 1fr); }

.sidenav {
  position: sticky; top: var(--topbar-h);
  height: calc(100vh - var(--topbar-h));
  overflow-y: auto; overscroll-behavior: contain;
  padding: 18px 14px 48px 16px;
  background: #faf9f5;
  border-right: 1px solid var(--line);
  font-size: 0.88rem; line-height: 1.55;
  scrollbar-width: thin;
}
.nav-home {
  display: block; padding: 6px 10px; margin-bottom: 10px; border-radius: 7px;
  color: var(--ink); text-decoration: none; font-weight: 700;
}
.nav-home:hover, .nav-home.is-current { background: var(--accent-soft); color: var(--accent); }
.nav-group { margin: 14px 0 6px; }
.nav-lecture {
  padding: 4px 10px; color: var(--ink); font-weight: 700; font-size: 0.92rem;
}
.nav-no { display: block; color: var(--accent-2); font-weight: 400; font-size: 0.78rem; letter-spacing: 0.06em; }
.nav-soon { margin: 2px 10px 0; color: var(--muted); font-size: 0.8rem; }
.nav-list { list-style: none; margin: 4px 0 0; padding: 0; }
.nav-link {
  display: flex; align-items: baseline; gap: 6px; padding: 5px 10px; border-radius: 7px;
  color: var(--ink-2); text-decoration: none;
}
.nav-link:hover { background: #f0ede5; color: var(--ink); }
.nav-link.is-current { background: var(--accent-soft); color: var(--accent); font-weight: 700; }
.nav-sec-no { flex: none; color: var(--muted); font-size: 0.8em; min-width: 1em; }
.nav-sec-title { flex: 1 1 auto; }
.nav-range { flex: none; color: var(--muted); font-size: 0.76em; font-weight: 400; }
.nav-slides { list-style: none; margin: 2px 0 8px 14px; padding: 0 0 0 10px; border-left: 1px solid var(--line-2); }
.nav-slide {
  display: flex; gap: 8px; padding: 4px 8px; border-radius: 6px;
  color: var(--ink-2); text-decoration: none; font-size: 0.84rem; line-height: 1.45;
}
.nav-slide:hover { background: #f0ede5; color: var(--ink); }
.nav-slide.is-active { background: #fff; color: var(--accent); box-shadow: inset 2px 0 0 var(--accent); }
.nav-slide.is-todo { color: var(--muted); }
.nav-pno { flex: none; min-width: 2.7em; color: var(--muted); font-size: 0.92em; font-variant-numeric: tabular-nums; }
.nav-review { font-size: 0.86rem; }
.nav-slide.is-active .nav-pno { color: var(--accent); }
.nav-check { display: none; flex: none; margin-left: auto; }
.nav-check svg { width: 14px; height: 14px; fill: none; stroke: var(--green); stroke-width: 2.4; stroke-linecap: round; stroke-linejoin: round; }
.nav-slide.is-done .nav-check { display: inline-flex; padding-top: 2px; }
.nav-done {
  flex: none; padding: 0 0.45em; border-radius: 999px; font-size: 0.72em; font-weight: 400;
  color: var(--green); background: #eef7ee; font-variant-numeric: tabular-nums;
}
.nav-done.is-complete { color: #fff; background: var(--green); }

.nav-scrim { display: none; }

@media (max-width: 1199px) {
  .layout { grid-template-columns: minmax(0, 1fr); }
  .sidenav {
    position: fixed; z-index: 70; left: 0; top: var(--topbar-h); bottom: 0; height: auto;
    width: min(86vw, 330px); transform: translateX(-102%);
    transition: transform 0.18s ease-out; box-shadow: 4px 0 18px rgba(20, 24, 33, 0.08);
  }
  body.nav-open .sidenav { transform: none; }
  body.nav-open .nav-scrim {
    display: block; position: fixed; inset: var(--topbar-h) 0 0 0; z-index: 65;
    background: rgba(20, 24, 33, 0.28);
  }
}

/* ------------------------------------------------------------------ */
/* 主区                                                                */
/* ------------------------------------------------------------------ */

.main { min-width: 0; }
.page { margin: 0 auto; padding: 32px 36px 96px; }
.page-section { max-width: 1520px; }
.page-article { max-width: 880px; }
@media (max-width: 760px) { .page { padding: 20px 16px 72px; } }

.kicker { color: var(--accent-2); font-size: 0.84rem; letter-spacing: 0.06em; }
.kicker-of { color: var(--muted); letter-spacing: 0; }

h1, h2, h3, h4 { font-family: var(--font-body); color: var(--ink); line-height: 1.4; }
h1 { font-size: 1.95rem; margin: 0.15em 0 0.3em; }

.section-head {
  max-width: 980px; padding: 6px 0 28px;
}
.section-intro { color: var(--ink-2); margin: 0.2em 0 1em; font-size: 1.04rem; }
.section-toc {
  list-style: none; margin: 0; padding: 14px 18px; display: grid; gap: 4px 28px;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  background: var(--paper); border: 1px solid var(--line); border-radius: var(--radius);
}
.section-toc a { display: flex; gap: 10px; color: var(--ink); text-decoration: none; padding: 3px 0; }
.section-toc a:hover { color: var(--accent); }
.toc-pno { flex: none; color: var(--muted); font-size: 0.86em; min-width: 3.6em; }
.section-tip { color: var(--muted); font-size: 0.88rem; margin: 12px 0 0; }

/* ---- 每一页课件：左图右文 ---- */

.slide-block {
  display: grid;
  grid-template-columns: minmax(320px, 42%) minmax(0, 1fr);
  gap: 0 44px;
  padding: 44px 0 64px;
  border-top: 1px solid var(--line);
  scroll-margin-top: calc(var(--topbar-h) + 4px);
}
.slide-col { min-width: 0; }
.slide-figure {
  position: sticky; top: calc(var(--topbar-h) + 20px);
  margin: 0;
}
.slide-zoom {
  position: relative; display: block; width: 100%; padding: 0; cursor: zoom-in;
  background: #fff; border: 1px solid var(--line-2); border-radius: 8px; overflow: hidden;
}
.slide-zoom img { display: block; width: 100%; height: auto; }
.zoom-hint {
  position: absolute; right: 8px; bottom: 8px; display: inline-flex; align-items: center; gap: 4px;
  padding: 2px 8px; border-radius: 6px; font-size: 0.78rem; color: #fff;
  background: rgba(29, 36, 51, 0.72); opacity: 0; transition: opacity 0.15s;
}
.slide-zoom:hover .zoom-hint, .slide-zoom:focus-visible .zoom-hint { opacity: 1; }
.slide-figure figcaption {
  display: flex; gap: 10px; align-items: baseline; margin-top: 8px;
  font-size: 0.86rem; color: var(--ink-2); line-height: 1.5;
}
.pno { flex: none; font-weight: 700; color: var(--ink); }
.ptitle { font-style: italic; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }

.notes { min-width: 0; max-width: 780px; }

@media (min-width: 1700px) {
  .slide-block { grid-template-columns: minmax(420px, 46%) minmax(0, 1fr); }
}
@media (max-width: 1023px) {
  .slide-block { grid-template-columns: minmax(0, 1fr); padding: 32px 0 48px; }
  .slide-figure { position: static; max-width: 680px; margin: 0 auto 22px; }
  .notes { max-width: none; }
}

.slide-head { margin-bottom: 1.2em; }
.slide-head h2 { font-size: 1.6rem; margin: 0.1em 0 0.15em; }
.slide-en { margin: 0; color: var(--ink-2); font-style: italic; }
.slide-summary {
  margin: 0.9em 0 0; padding: 0.65em 1em 0.7em;
  background: #fff8ef; border: 1px solid #f0dcc3; border-left: 4px solid var(--accent-2); border-radius: 8px;
}
.slide-summary p { margin: 0.35em 0 0; color: var(--ink); line-height: 1.8; }
.summary-tag {
  display: inline-block; padding: 0.06em 0.6em; border-radius: 4px;
  font-size: 0.78rem; font-weight: 700; letter-spacing: 0.04em; color: #fff; background: var(--accent-2);
}

/* 本页小标题：每个 ### 一枚，点击跳转 */
.slide-chips { display: flex; flex-wrap: wrap; align-items: center; gap: 6px; margin: 0.9em 0 0; }
.chips-label { margin-right: 2px; font-size: 0.8rem; color: var(--muted); }
.slide-chips a {
  display: inline-flex; align-items: center; padding: 0.12em 0.72em;
  border: 1px solid var(--line-2); border-radius: 999px; background: var(--paper);
  color: var(--ink-2); font-size: 0.84rem; line-height: 1.65; text-decoration: none;
}
.slide-chips a:hover { border-color: var(--accent); color: var(--accent); }
.slide-chips .katex { font-size: 1em; }

/* 这一页我看懂了 */
.understood-row {
  display: flex; flex-wrap: wrap; align-items: center; gap: 8px 14px;
  margin: 2.4em 0 0; padding-top: 1.1em; border-top: 1px dashed var(--line-2);
}
.understood-btn {
  display: inline-flex; align-items: center; gap: 8px; padding: 0.45em 1em; cursor: pointer;
  border: 1px solid var(--line-2); border-radius: 999px; background: var(--paper);
  color: var(--ink); font: inherit; font-size: 0.95rem;
}
.understood-btn:hover { border-color: var(--green); }
.ub-box {
  display: inline-grid; place-items: center; width: 18px; height: 18px;
  border: 1.5px solid var(--line-2); border-radius: 5px; background: #fff;
}
.ub-box svg { width: 13px; height: 13px; fill: none; stroke: #fff; stroke-width: 2.6; stroke-linecap: round; stroke-linejoin: round; }
.understood-btn[aria-pressed="true"] { border-color: var(--green); background: #eef7ee; color: #1f5f22; }
.understood-btn[aria-pressed="true"] .ub-box { border-color: var(--green); background: var(--green); }
.understood-note { font-size: 0.82rem; color: var(--muted); }

/* 专注阅读：隐藏课件栏，讲解居中加宽 */
.focus-toggle { display: none; }
.is-section .focus-toggle { display: inline-flex; }
.focus-toggle svg { width: 15px; height: 15px; fill: none; stroke: currentColor; stroke-width: 1.7; stroke-linejoin: round; }
.focus-toggle[aria-pressed="true"] { border-color: var(--accent); color: var(--accent); background: var(--accent-soft); }
.focus-mode .slide-block { grid-template-columns: minmax(0, 1fr); }
.focus-mode .slide-col { display: none; }
.focus-mode .notes { max-width: 860px; margin: 0 auto; width: 100%; }
@media (max-width: 760px) { .focus-toggle span { display: none; } }
.todo-note { color: var(--muted); font-style: italic; }

/* ---- 正文排版（讲解栏与文章页共用） ---- */

.notes, .prose { font-size: 1rem; }
.notes p, .prose p { margin: 0.8em 0; }
.notes h3, .prose h3 {
  font-size: 1.24rem; margin: 2.1em 0 0.7em; padding-left: 0.55em;
  border-left: 4px solid var(--accent-2); line-height: 1.35;
}
.notes h4, .prose h4 { font-size: 1.06rem; margin: 1.6em 0 0.4em; }
.prose h2 {
  font-size: 1.5rem; margin: 2.2em 0 0.6em; padding-bottom: 0.25em;
  border-bottom: 1px solid var(--line); scroll-margin-top: calc(var(--topbar-h) + 14px);
}
.notes ul, .notes ol, .prose ul, .prose ol { padding-left: 1.5em; margin: 0.6em 0; }
.notes li, .prose li { margin: 0.32em 0; }
.notes li > p, .prose li > p { margin: 0.3em 0; }
.notes strong, .prose strong { color: #111827; }
.notes blockquote, .prose blockquote {
  margin: 1em 0; padding: 0.2em 1em; color: var(--ink-2); border-left: 3px solid var(--line-2);
}
.notes code, .prose code {
  font-family: var(--font-mono); font-size: 0.88em; padding: 0.05em 0.35em;
  background: #f1efe9; border-radius: 4px;
}
hr { border: 0; border-top: 1px solid var(--line); margin: 2em 0; }

.en { font-style: italic; color: var(--ink-2); }
mark.hl { background: #fdecc8; color: inherit; padding: 0 0.15em; border-radius: 3px; }
.go { text-decoration-style: solid; }
.term {
  border-bottom: 1px dashed var(--accent); cursor: help;
  text-decoration: none;
}
.term:hover { color: var(--accent); }
.why {
  display: inline-block; margin: 0 0 0 0.4em; padding: 0 0.6em;
  font-size: 0.8em; line-height: 1.75; vertical-align: 0.06em;
  color: #0b5f54; background: #e2f2ee; border-radius: 999px;
}

/* KaTeX：构建时已排好，这里只调大小与长公式滚动 */
.katex { font-size: 1.07em; }
.katex-display { margin: 0.9em 0; padding: 0.15em 0; overflow-x: auto; overflow-y: hidden; }
.katex-display > .katex { font-size: 1.1em; }

/* 表格 */
.table-wrap { overflow-x: auto; margin: 1em 0; }
.table-wrap table { border-collapse: collapse; min-width: 100%; background: #fff; font-size: 0.95em; line-height: 1.7; }
.table-wrap th, .table-wrap td { border: 1px solid var(--line-2); padding: 0.45em 0.75em; vertical-align: top; }
.table-wrap th { background: #f3f1ea; font-weight: 700; }

/* 插图 */
.fig { width: var(--fig-w, 100%); margin: 1.5em auto; text-align: center; }
.fig img { display: block; width: 100%; height: auto; margin: 0 auto; }
.fig figcaption, .widget > figcaption {
  margin-top: 0.6em; font-size: 0.9rem; line-height: 1.65; color: var(--ink-2); text-align: left;
}
.fig-no { font-weight: 700; color: var(--ink); margin-right: 0.55em; }

/* 交互组件外框（组件内部样式在 widgets.css） */
.widget {
  margin: 1.6em 0; padding: 14px 14px 10px;
  background: var(--paper); border: 1px solid var(--line-2); border-radius: var(--radius);
}
.widget-stage { min-height: 120px; }
.widget-loading { margin: 0; padding: 2.2em 0; text-align: center; color: var(--muted); }
.widget-error { margin: 0; padding: 1.4em; text-align: center; color: var(--ink-2); background: #faf9f5; border-radius: 8px; }

/* ------------------------------------------------------------------ */
/* 方框                                                                */
/* ------------------------------------------------------------------ */

.box {
  --c: var(--navy); --b: #eef3fa;
  margin: 1.25em 0; background: var(--b);
  border: 1px solid rgba(29, 36, 51, 0.07); border-left: 4px solid var(--c); border-radius: 8px;
}
.box-head { display: flex; flex-wrap: wrap; align-items: baseline; gap: 4px 10px; padding: 0.6em 1.05em 0.1em; }
.box-tag {
  flex: none; padding: 0.05em 0.55em; border-radius: 4px;
  font-size: 0.76rem; letter-spacing: 0.08em; line-height: 1.6; color: #fff; background: var(--c);
}
.box-title { font-weight: 700; color: var(--ink); line-height: 1.5; }
.box-body { padding: 0.15em 1.05em 0.75em; }
.box-body > :first-child { margin-top: 0.35em; }
.box-body > :last-child { margin-bottom: 0.2em; }
.box .box { background: #fff; }

.box-def { --c: #1f4e8c; --b: #eef3fa; }
.box-prop { --c: #5b3f99; --b: #f3effa; }
.box-intuition { --c: #0f7b6c; --b: #eaf6f3; }
.box-example { --c: #2f7d32; --b: #eef7ee; }
.box-example .box-body { font-family: var(--font-kai); }
.box-pitfall { --c: #b26a00; --b: #fff6e8; }
.box-prereq { --c: #c2410c; --b: #fff1ea; }
.box-proof { --c: #475569; --b: #f4f6f9; }
.box-orig { --c: #6b7280; --b: #fafaf7; }
.box-orig .box-body { color: #2a303c; }
.box-note { --c: #0369a1; --b: #eef7fc; }
.box-check { --c: #b91c1c; --b: #fdf0f0; }
.box-summary { --c: #1f4e8c; --b: #f1f5fb; }
.box-quiz { --c: #7c3aed; --b: #f6f2fe; }

.box-proof ol > li { margin: 0.55em 0; }

details.answer { margin: 0.7em 0 0.2em; }
details.answer > summary {
  display: inline-flex; align-items: center; gap: 6px; cursor: pointer; list-style: none;
  padding: 0.15em 0.85em; border-radius: 999px; font-size: 0.9rem;
  color: #5b21b6; background: #fff; border: 1px solid #d9ccf7;
}
details.answer > summary::-webkit-details-marker { display: none; }
details.answer > summary::before { content: "▸"; font-size: 0.85em; transition: transform 0.15s; }
details.answer[open] > summary::before { transform: rotate(90deg); }
details.answer > summary:hover { border-color: #7c3aed; }
.answer-body {
  margin-top: 0.6em; padding: 0.3em 0.95em; background: #fff;
  border: 1px solid #e6dcfb; border-radius: 8px;
}

/* ------------------------------------------------------------------ */
/* 文章页、首页、导读页                                                  */
/* ------------------------------------------------------------------ */

.article-head { margin-bottom: 1.4em; }
.article-en { margin: 0; color: var(--ink-2); font-style: italic; }
.hero h1 { font-size: 2.2rem; }
.cards-title { font-size: 1.35rem; margin: 2.2em 0 0.8em; }

.page-toc {
  margin: 0 0 1.6em; padding: 12px 18px; background: var(--paper);
  border: 1px solid var(--line); border-radius: var(--radius); font-size: 0.94rem;
}
.page-toc-title { font-weight: 700; margin-bottom: 4px; }
.page-toc ol { margin: 0; padding-left: 1.4em; columns: 2; column-gap: 28px; }
.page-toc li { break-inside: avoid; }
@media (max-width: 640px) { .page-toc ol { columns: 1; } }

.sec-cards, .lec-cards { display: grid; gap: 16px; }
.lec-cards { grid-template-columns: repeat(auto-fill, minmax(250px, 1fr)); }
.sec-card, .lec-card, .tool-card {
  padding: 16px 20px; background: var(--paper);
  border: 1px solid var(--line); border-radius: var(--radius);
}
.sec-card-head { display: flex; align-items: baseline; gap: 10px; text-decoration: none; color: var(--ink); }
.sec-card-head:hover .sec-card-title { color: var(--accent); }
.sec-card-no {
  flex: none; width: 1.8em; height: 1.8em; display: inline-grid; place-items: center;
  border-radius: 50%; background: var(--accent); color: #fff; font-size: 0.85rem;
}
.sec-card-title { font-size: 1.15rem; font-weight: 700; }
.sec-card-intro { margin: 0.4em 0 0.6em; color: var(--ink-2); }
.sec-card-slides { list-style: none; margin: 0; padding: 0; display: grid; gap: 2px 22px; grid-template-columns: repeat(auto-fill, minmax(260px, 1fr)); font-size: 0.94rem; }
.sec-card-slides a { display: flex; gap: 8px; color: var(--ink); text-decoration: none; }
.sec-card-slides a:hover { color: var(--accent); }
.sec-card-slides .toc-pno { min-width: 1.8em; }

.lec-card h3 { margin: 0.1em 0 0; font-size: 1.2rem; }
.lec-card h3 a { color: var(--ink); text-decoration: none; }
.lec-card h3 a:hover { color: var(--accent); }
.lec-card-no { color: var(--accent-2); font-size: 0.84rem; letter-spacing: 0.06em; }
.lec-card-en { margin: 0.1em 0; color: var(--ink-2); font-style: italic; font-size: 0.92rem; }
.lec-card-meta { margin: 0.3em 0 0.4em; color: var(--muted); font-size: 0.86rem; }
.lec-card-secs { margin: 0; padding-left: 1.3em; font-size: 0.92rem; }
.lec-card.is-planned { background: #faf9f5; }
.lec-card.is-planned h3 { color: var(--ink-2); }
.tool-cards { display: grid; gap: 16px; grid-template-columns: repeat(auto-fill, minmax(250px, 1fr)); }
.tool-card h3 { margin: 0 0 0.3em; font-size: 1.1rem; }
.tool-card ol { margin: 0; padding-left: 1.3em; }

/* 术语表 */
.gl-filter {
  width: 100%; padding: 10px 14px; margin-bottom: 14px; font: inherit;
  border: 1px solid var(--line-2); border-radius: 8px; background: #fff;
}
.gl-list { list-style: none; margin: 0; padding: 0; display: grid; gap: 10px; }
.gl-item {
  padding: 12px 16px; background: var(--paper); border: 1px solid var(--line); border-radius: 8px;
  scroll-margin-top: calc(var(--topbar-h) + 14px);
}
.gl-item:target { border-color: var(--accent); box-shadow: inset 3px 0 0 var(--accent); }
.gl-head { display: flex; flex-wrap: wrap; gap: 4px 12px; align-items: baseline; }
.gl-zh { font-weight: 700; font-size: 1.05rem; }
.gl-en { color: var(--ink-2); font-style: italic; }
.gl-short { margin: 0.2em 0; }
.gl-where { font-size: 0.88rem; }

/* 翻页 */
.pager { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; margin-top: 48px; }
.pager-link {
  display: flex; flex-direction: column; padding: 12px 16px; text-decoration: none;
  background: var(--paper); border: 1px solid var(--line); border-radius: var(--radius); color: var(--ink);
}
.pager-link:hover { border-color: var(--accent); }
.pager-link.is-next { text-align: right; }
.pager-label { color: var(--muted); font-size: 0.84rem; }
.pager-title { font-weight: 700; }
@media (max-width: 640px) { .pager { grid-template-columns: 1fr; } }

/* ------------------------------------------------------------------ */
/* 浮层：灯箱、搜索、术语提示                                             */
/* ------------------------------------------------------------------ */

.lightbox {
  position: fixed; inset: 0; z-index: 100; display: grid; place-items: center;
  background: rgba(14, 18, 27, 0.9);
}
.lightbox[hidden] { display: none; }
.lb-figure { margin: 0; max-width: 94vw; text-align: center; }
.lb-figure img { display: block; max-width: 94vw; max-height: 86vh; width: auto; height: auto; background: #fff; border-radius: 4px; }
.lb-figure figcaption { margin-top: 10px; color: #e5e7eb; font-size: 0.92rem; }
.lb-btn {
  position: fixed; display: grid; place-items: center; width: 44px; height: 44px; border-radius: 50%;
  cursor: pointer; color: #fff; background: rgba(255, 255, 255, 0.12); border: 1px solid rgba(255, 255, 255, 0.25);
}
.lb-btn:hover { background: rgba(255, 255, 255, 0.22); }
.lb-btn svg { width: 22px; height: 22px; }
.lb-close { top: 16px; right: 16px; }
.lb-prev { left: 16px; top: 50%; transform: translateY(-50%); }
.lb-next { right: 16px; top: 50%; transform: translateY(-50%); }

.search-panel {
  position: fixed; inset: 0; z-index: 90; padding: 9vh 16px 16px;
  background: rgba(20, 24, 33, 0.38);
}
.search-panel[hidden] { display: none; }
.search-box {
  max-width: 720px; margin: 0 auto; background: #fff; border-radius: 12px;
  border: 1px solid var(--line-2); box-shadow: 0 12px 40px rgba(20, 24, 33, 0.18); overflow: hidden;
}
.search-input-row { display: flex; align-items: center; gap: 10px; padding: 12px 16px; border-bottom: 1px solid var(--line); }
.search-input-row svg { flex: none; color: var(--muted); }
.search-input-row input { flex: 1 1 auto; min-width: 0; border: 0; outline: 0; font: inherit; font-size: 1.05rem; background: transparent; }
.search-results { list-style: none; margin: 0; padding: 6px; max-height: 60vh; overflow-y: auto; }
.search-results li a {
  display: block; padding: 8px 12px; border-radius: 8px; color: var(--ink); text-decoration: none; line-height: 1.6;
}
.search-results li a.is-active, .search-results li a:hover { background: var(--accent-soft); }
.sr-title { display: block; font-weight: 700; }
.sr-meta { display: block; color: var(--muted); font-size: 0.82rem; }
.sr-snippet { display: block; color: var(--ink-2); font-size: 0.9rem; }
.search-results mark { background: #fde68a; color: inherit; border-radius: 2px; }
.search-empty { padding: 18px; color: var(--muted); text-align: center; }
.search-hint { margin: 0; padding: 8px 16px 12px; color: var(--muted); font-size: 0.82rem; border-top: 1px solid var(--line); }

.term-pop {
  position: absolute; z-index: 80; max-width: min(380px, 92vw); padding: 10px 14px;
  background: #fff; border: 1px solid var(--line-2); border-radius: 10px;
  box-shadow: 0 8px 24px rgba(20, 24, 33, 0.14); font-size: 0.92rem; line-height: 1.7;
}
.term-pop[hidden] { display: none; }
.tp-head { display: flex; flex-wrap: wrap; gap: 2px 10px; align-items: baseline; margin-bottom: 2px; }
.tp-zh { font-weight: 700; }
.tp-en { color: var(--ink-2); font-style: italic; }
.tp-where { display: inline-block; margin-top: 4px; font-size: 0.86rem; }

/* 手机上：课件图滚出屏幕后，右下角出现“看课件”按钮 */
.slide-fab {
  position: fixed; right: 14px; bottom: 16px; z-index: 40;
  display: inline-flex; align-items: center; gap: 6px; padding: 9px 15px; cursor: pointer;
  border: 0; border-radius: 999px; color: #fff; background: var(--accent);
  box-shadow: 0 4px 14px rgba(31, 78, 140, 0.32); font-size: 0.9rem; line-height: 1;
}
.slide-fab svg { width: 16px; height: 16px; fill: none; stroke: currentColor; stroke-width: 1.8; stroke-linecap: round; stroke-linejoin: round; }
.slide-fab[hidden] { display: none; }
@media (min-width: 1024px) { .slide-fab { display: none !important; } .focus-mode .slide-fab:not([hidden]) { display: inline-flex !important; } }

/* ------------------------------------------------------------------ */
/* 页组：一组课件页共用一段讲解                                          */
/* ------------------------------------------------------------------ */

.page-steps { display: flex; flex-wrap: wrap; align-items: center; gap: 4px; margin-top: 8px; }
.ps-label { margin-right: 4px; font-size: 0.8rem; color: var(--muted); }
.ps-btn {
  min-width: 2.3em; height: 27px; padding: 0 6px; cursor: pointer;
  border: 1px solid var(--line-2); border-radius: 6px; background: var(--paper);
  color: var(--ink-2); font-size: 0.82rem; line-height: 1; font-variant-numeric: tabular-nums;
}
.ps-btn:hover { border-color: var(--accent); color: var(--accent); }
.ps-btn[aria-pressed="true"] { background: var(--accent); border-color: var(--accent); color: #fff; }
.page-anchor { display: block; scroll-margin-top: calc(var(--topbar-h) + 14px); }

/* 讲解里的“课件第 N 页”分隔条：读到这里，左边的课件图换到这一页 */
.page-mark {
  display: flex; align-items: center; gap: 10px; margin: 2.2em 0 0.8em;
  scroll-margin-top: calc(var(--topbar-h) + 14px);
}
.page-mark::after { content: ""; flex: 1 1 auto; border-top: 1px dashed var(--line-2); }
.page-mark-btn {
  flex: none; display: inline-flex; align-items: center; gap: 6px; padding: 0.12em 0.8em; cursor: pointer;
  border: 1px solid #c9d6ea; border-radius: 999px; background: var(--accent-soft);
  color: var(--accent); font-size: 0.84rem; line-height: 1.7;
}
.page-mark-btn::before { content: "▣"; font-size: 0.86em; }
.page-mark-btn:hover { border-color: var(--accent); }

/* ------------------------------------------------------------------ */
/* 新方框：定理、推论、算法步骤、逐步推导                                  */
/* ------------------------------------------------------------------ */

.box-thm { --c: #5b3f99; --b: #f3effa; }
.box-cor { --c: #7c5cbf; --b: #f6f2fc; }
.box-algorithm { --c: #0e7490; --b: #ebf6f9; }
.box-algorithm ol > li { margin: 0.5em 0; }
.box-steps { --c: #9a3412; --b: #fff7f1; }
.box-steps .box-body { counter-reset: step; }
.step { counter-increment: step; margin: 0.7em 0; padding: 0.45em 0.9em 0.5em; background: #fff; border: 1px solid #f1dccd; border-radius: 8px; }
.step::before {
  content: "第 " counter(step) " 步"; display: inline-block; margin-bottom: 0.1em; padding: 0 0.55em;
  font-size: 0.76rem; letter-spacing: 0.04em; line-height: 1.7; color: #fff; background: var(--c); border-radius: 4px;
}
.step-title { display: inline; margin-left: 0.5em; font-weight: 700; }
.step-body > :first-child { margin-top: 0.3em; }
.step-body > :last-child { margin-bottom: 0.1em; }
.steps-js .step.is-hidden { display: none; }
.steps-ctrl { display: flex; flex-wrap: wrap; align-items: center; gap: 6px 8px; margin: 0.6em 0 0.2em; }
.steps-ctrl .w-btn:disabled { opacity: 0.45; cursor: default; }
.steps-count { color: var(--muted); font-size: 0.84rem; }

/* ------------------------------------------------------------------ */
/* 复习页：自测汇总（错题本）与定义速查                                     */
/* ------------------------------------------------------------------ */

.rv-toolbar {
  position: sticky; top: calc(var(--topbar-h) + 6px); z-index: 5;
  display: flex; flex-wrap: wrap; align-items: center; gap: 8px 12px; margin: 0 0 1.2em; padding: 10px 12px;
  background: var(--paper); border: 1px solid var(--line); border-radius: var(--radius);
}
.rv-count { color: var(--ink-2); font-size: 0.86rem; }
.rv-sec { font-size: 1.25rem; margin: 1.8em 0 0.6em; }
.rv-item, .sh-item { margin: 0 0 1.4em; padding: 4px 16px 12px; background: var(--paper); border: 1px solid var(--line); border-radius: var(--radius); }
.rv-item[data-mark="bad"] { border-left: 4px solid var(--red); }
.rv-item[data-mark="ok"] { border-left: 4px solid var(--green); }
.rv-meta { display: flex; flex-wrap: wrap; justify-content: space-between; gap: 4px 12px; margin: 8px 0 -4px; font-size: 0.86rem; }
.rv-src { color: var(--ink-2); }
.rv-state { color: var(--muted); }
.rv-item[data-mark="bad"] .rv-state { color: var(--red); font-weight: 700; }
.rv-item[data-mark="ok"] .rv-state { color: var(--green); font-weight: 700; }
.rv-mark { display: flex; gap: 8px; }
.rv-mark .rv-btn[data-mark="ok"][aria-pressed="true"] { background: var(--green); border-color: var(--green); }
.rv-mark .rv-btn[data-mark="bad"][aria-pressed="true"] { background: var(--red); border-color: var(--red); }
.rv-backup { display: flex; flex-wrap: wrap; align-items: center; gap: 8px; margin-top: 2em; font-size: 0.9rem; color: var(--ink-2); }
.rv-import { cursor: pointer; }

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { transition: none !important; }
}

@media print {
  .topbar, .sidenav, .pager, .section-tip, .zoom-hint, .page-steps, .steps-ctrl, .understood-row,
  .rv-toolbar, .rv-mark, .rv-backup, .sh-print, .slide-fab { display: none !important; }
  .layout { display: block; }
  .slide-block { grid-template-columns: 38% 1fr; break-inside: avoid-page; }
  .slide-figure { position: static; }
  details.answer > .answer-body { display: block; }
  .steps-js .step.is-hidden { display: block; }
  .sh-item { break-inside: avoid; }
}