:root {
  --ink: #173239;
  --paper: #fffdf6;
  --canvas: #e9e4d8;
  --teal: #0f7773;
  --gold: #e2a42d;
  --coral: #d6694a;
  --line: #cbbfa9;
  --soft: #f5eedf;
}

html { scroll-behavior: smooth; }
body {
  max-width: 1180px;
  margin: 0 auto;
  padding: 42px 34px 100px 320px;
  background:
    linear-gradient(rgba(23, 50, 57, .035) 1px, transparent 1px),
    linear-gradient(90deg, rgba(23, 50, 57, .035) 1px, transparent 1px),
    var(--canvas);
  background-size: 28px 28px;
  color: var(--ink);
  font-family: "FZKai-Z03", "Kaiti SC", "STKaiti", "PingFang SC", sans-serif;
  line-height: 1.78;
}

body > h1, body > h2, body > p, body > blockquote, body > ul {
  max-width: 1100px;
}

h1 {
  margin: 0 0 18px;
  padding: 28px 32px;
  border: 3px solid var(--ink);
  border-radius: 22px;
  background: var(--paper);
  box-shadow: 8px 9px 0 rgba(23, 50, 57, .14);
  font-size: clamp(28px, 4vw, 46px);
  line-height: 1.15;
}

body > h2 {
  margin: 76px 0 20px;
  padding-bottom: 10px;
  border-bottom: 4px solid var(--gold);
  font-size: clamp(25px, 3vw, 34px);
}

blockquote {
  margin: 18px 0 30px;
  padding: 14px 18px;
  border-left: 6px solid var(--gold);
  background: #fff8df;
}

nav#TOC {
  position: fixed;
  z-index: 10;
  top: 24px;
  bottom: 24px;
  left: max(20px, calc(50vw - 590px));
  width: 270px;
  overflow: auto;
  padding: 18px 20px;
  border: 2px solid var(--ink);
  border-radius: 18px;
  background: rgba(255, 253, 246, .97);
  box-shadow: 6px 7px 0 rgba(23, 50, 57, .13);
}

nav#TOC::before {
  content: "30 节视频归档";
  display: block;
  margin-bottom: 12px;
  color: var(--teal);
  font-weight: 900;
}

nav#TOC ul { margin: 0; padding-left: 18px; }
nav#TOC > ul { padding-left: 0; list-style: none; }
nav#TOC a { color: var(--ink); font-size: 13px; text-decoration: none; }
nav#TOC a:hover, nav#TOC a:focus-visible { color: var(--coral); text-decoration: underline; }

.video-lesson {
  display: grid;
  grid-template-columns: minmax(310px, .9fr) minmax(390px, 1.1fr);
  gap: 30px;
  align-items: start;
  margin-bottom: 70px;
  padding: 26px;
  border: 2px solid var(--ink);
  border-radius: 24px;
  background: var(--paper);
  box-shadow: 9px 10px 0 rgba(23, 50, 57, .13);
}

.video-visual {
  position: sticky;
  top: 24px;
}

.video-visual figure {
  margin: 0 0 14px;
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: 15px;
  background: var(--soft);
}

.video-visual img {
  display: block;
  width: 100%;
  aspect-ratio: 16 / 9;
  object-fit: cover;
}

.video-visual figcaption {
  padding: 8px 12px;
  color: #617275;
  font-size: 12px;
  text-align: center;
}

.video-visual > p {
  margin: 8px 0;
  color: #56696c;
  font-size: 13px;
}

.video-visual h3, .video-script h3 {
  margin: 20px 0 12px;
  color: var(--teal);
  font-size: 20px;
}

.video-visual ol {
  padding-left: 22px;
  font-size: 14px;
}

.video-script {
  padding: 22px 24px;
  border-left: 7px solid var(--teal);
  border-radius: 0 16px 16px 0;
  background: var(--soft);
}

.video-script h3 { margin-top: 0; }
.video-script h3:not(:first-child) {
  margin-top: 30px;
  padding-top: 22px;
  border-top: 2px dashed var(--line);
  color: var(--coral);
}
.video-script p {
  margin: 0 0 14px;
  font-size: 17px;
  line-height: 1.9;
}
.video-script blockquote {
  margin: 14px 0;
  padding: 14px 16px;
  border-left: 5px solid var(--gold);
  background: #fff9e8;
  color: #4c5e61;
  font-size: 14px;
}

a { color: var(--teal); font-weight: 700; }

@media (max-width: 980px) {
  body { padding: 24px 18px 80px; }
  nav#TOC {
    position: static;
    width: auto;
    max-height: 320px;
    margin-bottom: 28px;
  }
  .video-lesson { grid-template-columns: 1fr; }
  .video-visual { position: static; }
}

@media (max-width: 560px) {
  .video-lesson { padding: 16px; }
  .video-script { padding: 17px; }
  .video-script p { font-size: 16px; }
}

@media print {
  body { padding: 0; background: white; }
  nav#TOC, .course-back-to-index { display: none !important; }
  .video-lesson { break-inside: avoid; box-shadow: none; }
  .video-visual { position: static; }
}