:root {
  --bg: #f6f8fb;
  --card: #fff;
  --text: #1a1a1a;
  --muted: #5f6368;
  --accent: #0b57d0;
  --accent-soft: #e8f0fe;
  --warn-bg: #fff8e1;
  --warn-border: #f9a825;
  --border: #e0e4ea;
  --radius: 10px;
  --shadow: 0 1px 3px rgba(0,0,0,.08);
}
* { box-sizing: border-box; }
body {
  margin: 0;
  font-family: "Segoe UI", "Microsoft JhengHei", sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.55;
}
a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }
.wrap { max-width: 1100px; margin: 0 auto; padding: 1.5rem 1.25rem 3rem; }
.hero {
  background: linear-gradient(135deg, #0b57d0 0%, #1a73e8 45%, #34a853 100%);
  color: #fff;
  padding: 2.5rem 1.25rem 2rem;
}
.hero .wrap { padding-top: 0; padding-bottom: 0; }
.hero h1 { margin: 0; font-size: 1.85rem; font-weight: 700; }
.hero-title-row {
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  gap: .45rem .75rem;
  margin: 0 0 .4rem;
}
.hero-updated {
  font-size: .9rem;
  font-weight: 500;
  opacity: .95;
  background: rgba(255,255,255,.22);
  border: 1px solid rgba(255,255,255,.3);
  border-radius: 6px;
  padding: .18rem .55rem;
  white-space: nowrap;
}
.hero-updated time { font-weight: 600; }
.hero p { margin: .35rem 0; opacity: .95; }
.hero .links a { color: #fff; font-weight: 600; }
.stats {
  display: flex; flex-wrap: wrap; gap: .75rem; margin: 1.25rem 0 0;
}
.stat {
  background: rgba(255,255,255,.15);
  border-radius: 8px;
  padding: .55rem .9rem;
  font-size: .92rem;
}
.stat-updated {
  background: rgba(255,255,255,.28);
  font-weight: 600;
  border: 1px solid rgba(255,255,255,.35);
}
.notice {
  margin: 1.25rem 0;
  padding: .85rem 1rem;
  background: var(--warn-bg);
  border-left: 4px solid var(--warn-border);
  border-radius: 6px;
  color: #5f4339;
  font-size: .95rem;
}
.toolbar {
  display: flex; flex-wrap: wrap; gap: .75rem; align-items: center;
  margin: 1.5rem 0 1rem;
}
#search {
  flex: 1 1 220px;
  padding: .65rem .85rem;
  border: 1px solid var(--border);
  border-radius: 8px;
  font-size: 1rem;
}
.filters { display: flex; flex-wrap: wrap; gap: .4rem; }
.filter-btn {
  border: 1px solid var(--border);
  background: var(--card);
  border-radius: 999px;
  padding: .35rem .85rem;
  cursor: pointer;
  font-size: .88rem;
}
.filter-btn.active {
  background: var(--accent-soft);
  border-color: var(--accent);
  color: var(--accent);
  font-weight: 600;
}
.course-block {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  margin: 1.25rem 0;
  overflow: hidden;
}
.course-block h2 {
  margin: 0;
  padding: .85rem 1rem;
  font-size: 1.15rem;
  background: #f8fafc;
  border-bottom: 1px solid var(--border);
}
.lesson-table { width: 100%; border-collapse: collapse; }
.lesson-table th, .lesson-table td {
  text-align: left;
  padding: .55rem 1rem;
  border-bottom: 1px solid #eef1f5;
  vertical-align: top;
}
.lesson-table th { font-size: .82rem; color: var(--muted); font-weight: 600; }
.lesson-table tr:hover td { background: #f8fbff; }
.badge {
  display: inline-block;
  font-size: .75rem;
  padding: .12rem .45rem;
  border-radius: 4px;
  background: #e8f5e9;
  color: #2e7d32;
}
.badge.muted { background: #f1f3f4; color: #5f6368; }
.badge.warn { background: #fff3e0; color: #e65100; border: 1px solid #ffcc80; }
.notice-sync {
  margin: .75rem 0 0;
  padding: .7rem .9rem;
  background: #fff3e0;
  border-left: 4px solid #fb8c00;
  border-radius: 6px;
  color: #5d4037;
  font-size: .92rem;
}
.empty { color: var(--muted); padding: 1rem; }
.foot { color: var(--muted); font-size: .88rem; margin-top: 2rem; }

/* lesson page */
.lesson-hero { padding: 1.25rem 0 .5rem; }
.lesson-hero h1 { margin: 0 0 .35rem; font-size: 1.45rem; }
.meta { color: var(--muted); font-size: .92rem; }
.player-stack {
  border-radius: var(--radius);
  overflow: hidden;
  box-shadow: var(--shadow);
  background: #000;
  margin: 1rem 0;
}
.player-stack .yt-wrap {
  position: relative;
  width: 100%;
  padding-bottom: 56.25%;
  height: 0;
}
.player-stack #yt-player-mount {
  position: absolute;
  top: 0; left: 0;
  width: 100%; height: 100%;
}
.player-stack .yt-iframe {
  position: absolute;
  top: 0; left: 0;
  width: 100%; height: 100%;
  border: 0;
}
.yt-fallback {
  position: absolute;
  inset: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 1.25rem;
  background: #1e1e1e;
  color: #e8eaed;
  text-align: center;
  font-size: .95rem;
}
.yt-fallback p { margin: .4rem 0; }
.yt-fallback a { color: #8ab4f8; }
.subtitle-bar {
  display: flex; align-items: flex-start; gap: .75rem;
  min-height: 3rem; padding: .7rem 1rem;
  background: #1e1e1e; color: #f5f5f5;
}
.subtitle-bar .subtitle-time {
  flex-shrink: 0; color: #9aa0a6; font-size: .85em;
  font-variant-numeric: tabular-nums;
}
.subtitle-bar .subtitle-text { flex: 1; line-height: 1.45; }
.transcript-wrap { margin: 1.5rem 0 2rem; }
.transcript-wrap h2 { font-size: 1.1rem; margin-bottom: .5rem; }
.transcript-wrap .hint { font-size: .85em; font-weight: normal; color: var(--muted); }
.transcript-viewport {
  height: 16rem; overflow-y: auto;
  border: 1px solid var(--border);
  border-radius: 8px;
  background: var(--card);
}
.seg {
  padding: .45rem .85rem;
  cursor: pointer;
  border-left: 3px solid transparent;
}
.seg:hover { background: #f5f8ff; }
.seg.active { background: #fff8e1; border-left-color: var(--warn-border); }
.seg .time {
  color: var(--muted); font-size: .85em;
  margin-right: .55rem;
  font-variant-numeric: tabular-nums;
}
.nav-top { margin-bottom: 1rem; font-size: .95rem; }
@media (max-width: 640px) {
  .lesson-table th:nth-child(3), .lesson-table td:nth-child(3) { display: none; }
}