/* Shared stylesheet for all lecture note pages */
:root {
  --ink: #1a2332;
  --ink-soft: #4a5568;
  --accent: #0b66c3;
  --accent-soft: #e8f1fb;
  --card: #ffffff;
  --bg: #f4f6f9;
  --border: #dde3ea;
  --warn-bg: #fff7e6;
  --warn-border: #f0c36d;
  --code-bg: #f0f2f5;
}
* { box-sizing: border-box; }
body {
  margin: 0;
  font-family: "Segoe UI", "Microsoft YaHei", "PingFang SC", sans-serif;
  color: var(--ink);
  background: var(--bg);
  line-height: 1.75;
}
.page { max-width: 980px; margin: 0 auto; padding: 0 24px 80px; }
header.course {
  background: linear-gradient(135deg, #0b3d91 0%, #0b66c3 100%);
  color: #fff;
  padding: 36px 24px 28px;
  margin: 0 -24px 28px;
}
header.course h1 { margin: 0 0 6px; font-size: 1.7em; }
header.course .meta { opacity: .85; font-size: .95em; }
header.course a { color: #cfe3ff; }
nav.toc {
  background: var(--card); border: 1px solid var(--border); border-radius: 10px;
  padding: 14px 22px; margin-bottom: 28px; font-size: .95em;
}
nav.toc ol { margin: 6px 0; padding-left: 22px; }
nav.toc a { color: var(--accent); text-decoration: none; }
nav.toc a:hover { text-decoration: underline; }
section.topic {
  background: var(--card); border: 1px solid var(--border); border-radius: 10px;
  padding: 8px 26px 18px; margin-bottom: 24px;
}
section.topic h2 {
  font-size: 1.25em; border-bottom: 2px solid var(--accent-soft);
  padding-bottom: 8px; margin-top: 18px;
}
section.topic h3 { font-size: 1.05em; color: var(--accent); margin: 18px 0 6px; }
.ts {
  display: inline-block; background: var(--accent-soft); color: var(--accent);
  border-radius: 5px; padding: 0 8px; font-size: .82em; font-family: Consolas, monospace;
  text-decoration: none; vertical-align: middle; margin-left: 6px; white-space: nowrap;
}
.ts:hover { background: var(--accent); color: #fff; }
figure {
  margin: 14px 0; background: #fafbfc; border: 1px solid var(--border);
  border-radius: 8px; padding: 10px; text-align: center;
}
figure img { max-width: 100%; border-radius: 4px; }
figcaption { font-size: .88em; color: var(--ink-soft); margin-top: 8px; text-align: left; }
.callout {
  background: var(--warn-bg); border-left: 4px solid var(--warn-border);
  border-radius: 6px; padding: 10px 16px; margin: 14px 0; font-size: .95em;
}
.kpoints { background: var(--accent-soft); border-radius: 8px; padding: 14px 22px; }
.kpoints li { margin: 6px 0; }
table { border-collapse: collapse; width: 100%; margin: 12px 0; font-size: .93em; }
th, td { border: 1px solid var(--border); padding: 7px 12px; text-align: left; }
th { background: var(--accent-soft); }
code { background: var(--code-bg); border-radius: 4px; padding: 1px 6px; font-family: Consolas, monospace; font-size: .9em; }
.footer-nav { display: flex; justify-content: space-between; margin-top: 36px; font-size: .95em; }
.footer-nav a { color: var(--accent); text-decoration: none; }
/* index page cards */
.lecture-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(280px, 1fr)); gap: 16px; }
.lecture-card {
  background: var(--card); border: 1px solid var(--border); border-radius: 10px;
  padding: 18px 20px; text-decoration: none; color: var(--ink); display: block;
  transition: box-shadow .15s, transform .15s;
}
.lecture-card:hover { box-shadow: 0 4px 14px rgba(11,102,195,.18); transform: translateY(-2px); }
.lecture-card .num { color: var(--accent); font-weight: 700; font-size: .85em; }
.lecture-card h3 { margin: 4px 0 6px; font-size: 1.05em; }
.lecture-card .desc { font-size: .88em; color: var(--ink-soft); }