:root {
  --bg: #fdfdfc;
  --text: #24292f;
  --muted: #57606a;
  --accent: #8c1515;
  --border: #e4e4e1;
  --code-bg: #f6f6f4;
  --card-bg: #ffffff;
}
* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  font-family: "PingFang SC", "Hiragino Sans GB", "Noto Sans CJK SC", "Source Han Sans SC", -apple-system, "Segoe UI", sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.8;
  font-size: 17px;
}
.container { max-width: 860px; margin: 0 auto; padding: 24px 20px 80px; }

/* 顶部导航 */
.topnav {
  position: sticky; top: 0; z-index: 10;
  background: rgba(253, 253, 252, 0.92);
  backdrop-filter: blur(6px);
  border-bottom: 1px solid var(--border);
  display: flex; align-items: center; justify-content: space-between;
  padding: 10px 20px;
}
.topnav .brand { font-weight: 700; color: var(--accent); text-decoration: none; font-size: 16px; }
.topnav .crumb { color: var(--muted); font-size: 14px; }

h1 { font-size: 1.9em; margin: 1.2em 0 0.4em; line-height: 1.4; }
h2 {
  font-size: 1.4em; margin: 2.2em 0 0.6em;
  padding-bottom: 0.25em; border-bottom: 1px solid var(--border);
}
h3 { font-size: 1.15em; margin: 1.6em 0 0.4em; }
p { margin: 0.7em 0; }
a { color: var(--accent); }
.subtitle { color: var(--muted); margin-top: 0; }

/* 摘要框 */
.lecture-meta {
  background: var(--card-bg); border: 1px solid var(--border); border-radius: 10px;
  padding: 14px 18px; margin: 1.2em 0;
}
.lecture-meta b { color: var(--accent); }

/* 重点讲解块 */
.deep-dive {
  background: #fbf7f0; border-left: 4px solid var(--accent);
  border-radius: 0 8px 8px 0; padding: 14px 18px; margin: 1.4em 0;
}
.deep-dive .tag {
  display: inline-block; font-size: 12px; font-weight: 700; color: #fff;
  background: var(--accent); border-radius: 4px; padding: 1px 8px; margin-bottom: 6px;
  letter-spacing: 1px;
}
/* 拓展块 */
.extension {
  background: #f0f6f3; border-left: 4px solid #2e7d5b;
  border-radius: 0 8px 8px 0; padding: 14px 18px; margin: 1.4em 0;
}
.extension .tag {
  display: inline-block; font-size: 12px; font-weight: 700; color: #fff;
  background: #2e7d5b; border-radius: 4px; padding: 1px 8px; margin-bottom: 6px;
  letter-spacing: 1px;
}
/* 关键概念 */
.keypoint {
  background: #f4f1fa; border-left: 4px solid #5b4b8a;
  border-radius: 0 8px 8px 0; padding: 12px 18px; margin: 1.2em 0;
}

/* 数学公式 */
.formula {
  text-align: center; font-family: "STIX Two Math", Georgia, serif;
  font-size: 1.1em; margin: 1em 0; overflow-x: auto;
}

code {
  font-family: "SF Mono", Menlo, Consolas, monospace;
  background: var(--code-bg); border-radius: 4px; padding: 1px 6px; font-size: 0.88em;
}
pre {
  background: var(--code-bg); border: 1px solid var(--border); border-radius: 8px;
  padding: 14px 16px; overflow-x: auto; line-height: 1.6;
}
pre code { background: none; padding: 0; font-size: 0.9em; }

/* highlight.js 代码高亮配色（GitHub 风格，调校至本站暖色浅色主题） */
.hljs-comment, .hljs-quote { color: #7d776d; font-style: italic; }
.hljs-keyword, .hljs-selector-tag, .hljs-deletion { color: #cf222e; }
.hljs-string, .hljs-regexp, .hljs-addition { color: #0a3069; }
.hljs-number, .hljs-literal, .hljs-built_in, .hljs-symbol, .hljs-link { color: #0550ae; }
.hljs-title, .hljs-section, .hljs-name, .hljs-selector-id, .hljs-selector-class { color: #8250df; }
.hljs-attr, .hljs-attribute, .hljs-variable, .hljs-template-variable, .hljs-property, .hljs-params { color: #953800; }
.hljs-type, .hljs-title.class_, .hljs-class .hljs-title { color: #116329; }
.hljs-meta { color: var(--muted); }
.hljs-emphasis { font-style: italic; }
.hljs-strong { font-weight: 700; }

/* mermaid 图：渲染后为 svg，容器居中 */
pre.mermaid {
  text-align: center; line-height: 1.4;
  display: flex; justify-content: center;
  overflow-x: auto;
}
pre.mermaid svg { max-width: 100%; height: auto; }
/* 点击放大（灯箱逻辑在 viewer.mjs）：悬停出提示角标 */
pre.mermaid { position: relative; cursor: zoom-in; }
pre.mermaid:hover { border-color: #c9c5bd; }
pre.mermaid::after {
  content: "🔍 放大";
  position: absolute; top: 8px; right: 10px;
  font-size: 12px; color: var(--muted);
  opacity: 0; transition: opacity .15s; pointer-events: none;
}
pre.mermaid:hover::after { opacity: .9; }

/* mermaid 灯箱：白纸承图（图的配色是浅色，深底会看不清），底部工具条 */
.diagram-lightbox {
  position: fixed; inset: 0; z-index: 100;
  background: rgba(36, 41, 47, 0.82);
  display: none;
}
.diagram-lightbox.open { display: block; }
.lb-canvas { position: absolute; inset: 0; overflow: hidden; }
.lb-paper {
  position: absolute; left: 0; top: 0; padding: 24px;
  background: #fff; border-radius: 12px; box-shadow: 0 16px 48px rgba(0, 0, 0, 0.45);
  transform-origin: 0 0; cursor: grab; user-select: none; touch-action: none;
}
.lb-paper.dragging { cursor: grabbing; }
.lb-paper svg { display: block; }
.lb-bar {
  position: absolute; left: 50%; bottom: 22px; transform: translateX(-50%);
  display: flex; align-items: center; gap: 2px;
  background: rgba(253, 253, 252, 0.95); border: 1px solid var(--border); border-radius: 999px;
  padding: 4px 6px; box-shadow: 0 4px 16px rgba(0, 0, 0, 0.25);
}
.lb-bar button {
  font: inherit; font-size: 15px; line-height: 1; color: var(--text);
  background: none; border: none; border-radius: 999px;
  min-width: 34px; height: 30px; padding: 0 10px; cursor: pointer;
}
.lb-bar button:hover { background: var(--code-bg); color: var(--accent); }
.lb-scale { min-width: 44px; text-align: center; font-size: 12.5px; color: var(--muted); }

blockquote {
  margin: 1em 0; padding: 4px 18px; color: var(--muted);
  border-left: 3px solid var(--border);
}

table { border-collapse: collapse; width: 100%; margin: 1.2em 0; font-size: 0.95em; }
th, td { border: 1px solid var(--border); padding: 8px 12px; text-align: left; }
th { background: var(--code-bg); }

figure { margin: 1.4em 0; text-align: center; }
figcaption { color: var(--muted); font-size: 0.9em; margin-top: 6px; }

/* 上一讲/下一讲 */
.pager {
  display: flex; justify-content: space-between; gap: 12px;
  margin-top: 3em; border-top: 1px solid var(--border); padding-top: 18px;
}
.pager a {
  text-decoration: none; color: var(--text);
  background: var(--card-bg); border: 1px solid var(--border); border-radius: 8px;
  padding: 10px 16px; max-width: 48%;
}
.pager a:hover { border-color: var(--accent); }
.pager .dir { display: block; font-size: 12px; color: var(--muted); }

/* 课程页讲次列表 */
.lecture-list { list-style: none; padding: 0; margin: 1.5em 0; }
.lecture-list li {
  display: flex; align-items: center;
  background: var(--card-bg); border: 1px solid var(--border); border-radius: 10px;
  margin-bottom: 10px; transition: border-color .15s;
}
.lecture-list li:hover { border-color: var(--accent); }
.lecture-list li > a {
  flex: 1; min-width: 0;
  display: flex; align-items: baseline; gap: 14px;
  text-decoration: none; color: var(--text); padding: 12px 18px;
}
/* 播放按钮：固定在卡片右端的圆形图标，各行对齐成一列 */
.lecture-list a.yt {
  flex: none; padding: 0;
  display: inline-flex; align-items: center; justify-content: center;
  width: 30px; height: 30px; margin-right: 14px;
  border: 1px solid var(--border); border-radius: 50%;
  color: var(--accent); text-decoration: none; font-size: 12px; line-height: 1;
  transition: background .15s, color .15s, border-color .15s;
}
.lecture-list li:hover a.yt { border-color: var(--accent); }
.lecture-list a.yt:hover { background: var(--accent); border-color: var(--accent); color: #fff; }
.lecture-list .num { font-weight: 700; color: var(--accent); min-width: 2.2em; }
.lecture-list .desc { color: var(--muted); font-size: 0.9em; margin-left: auto; text-align: right; }

/* ── 总站主页：hero + 分类课程卡片 ── */
.container-wide { max-width: 1080px; }
.home-hero h1 { margin: 0.9em 0 0.3em; }
.home-hero .subtitle { max-width: 44em; }
.home-stats { display: flex; flex-wrap: wrap; gap: 8px; margin: 1.2em 0 0; }
.home-stats span {
  background: var(--card-bg); border: 1px solid var(--border); border-radius: 999px;
  padding: 2px 14px; font-size: 14px; color: var(--muted);
}

/* 分类速览芯片（平滑滚动，viewer.mjs 委托处理） */
.cat-nav { display: flex; flex-wrap: wrap; gap: 8px; margin-top: 1.4em; }
.cat-chip {
  font: inherit; font-size: 14px; color: var(--text);
  background: var(--card-bg); border: 1px solid var(--border); border-radius: 999px;
  padding: 4px 14px; cursor: pointer;
  transition: border-color .15s, color .15s;
}
.cat-chip:hover { border-color: var(--accent); color: var(--accent); }

/* 分类小节标题 */
.cat-heading { scroll-margin-top: 64px; margin: 2em 0 0.8em; display: flex; align-items: baseline; gap: 12px; }
.cat-count { font-size: 13px; font-weight: 400; color: var(--muted); }

/* 课程卡片网格 */
.course-grid {
  display: grid; grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: 14px;
}
.course-card {
  display: flex; flex-direction: column;
  background: var(--card-bg); border: 1px solid var(--border); border-radius: 12px;
  padding: 15px 18px 14px;
  text-decoration: none; color: var(--text);
  transition: border-color .15s, box-shadow .15s, transform .15s;
}
.course-card:hover {
  border-color: var(--accent);
  box-shadow: 0 4px 14px rgba(140, 21, 21, 0.08);
  transform: translateY(-2px);
}
.course-card .card-top { display: flex; justify-content: space-between; align-items: center; }
.course-card .card-badge {
  font-size: 12px; font-weight: 700; color: var(--accent); letter-spacing: 1px;
  background: rgba(140, 21, 21, 0.07); border-radius: 4px; padding: 1px 8px;
}
.course-card .card-count { font-size: 13px; color: var(--muted); }
.course-card .card-name { font-size: 1.25em; font-weight: 700; margin-top: 8px; line-height: 1.3; }
.course-card:hover .card-name { color: var(--accent); }
.course-card .card-title { font-weight: 600; margin-top: 2px; }
.course-card .card-meta { font-size: 13px; color: var(--muted); margin-top: 4px; }
.course-card .card-intro {
  font-size: 14px; color: var(--muted); margin-top: 10px; line-height: 1.7;
  display: -webkit-box; -webkit-box-orient: vertical; -webkit-line-clamp: 2;
  overflow: hidden;
}

/* 课程页「返回总目录」胶囊按钮（页首 + 列表末尾各一个） */
.back-bar {
  display: inline-flex; align-items: center; gap: 8px;
  margin: 18px 0 -4px;
  background: var(--card-bg); border: 1px solid var(--border); border-radius: 999px;
  padding: 5px 16px 5px 13px;
  font-size: 14px; color: var(--text); text-decoration: none;
  transition: border-color .15s, box-shadow .15s;
}
.back-bar:hover { border-color: var(--accent); box-shadow: 0 2px 8px rgba(140, 21, 21, 0.08); }
.back-bar .back-arrow {
  color: var(--accent); font-weight: 700; font-size: 17px; line-height: 1;
  transform: translateY(-1px); transition: transform .15s;
}
.back-bar:hover .back-arrow { transform: translate(-2px, -1px); }
.back-bar .back-ctx {
  font-size: 12.5px; color: var(--muted);
  padding-left: 9px; margin-left: 2px; border-left: 1px solid var(--border);
}
.back-bar.back-bar-end { margin: 2.4em 0 0.6em; }

/* viewer 加载态与错误卡片 */
.loading { color: var(--muted); }
.error {
  background: #fdf0f0; border: 1px solid #e8c2c2; border-left: 4px solid var(--accent);
  border-radius: 0 8px 8px 0; padding: 14px 18px; margin: 2em 0;
}
.error b { color: var(--accent); display: block; margin-bottom: 4px; }
.error p { margin: 0.4em 0; }