:root {
  --ink: #111722;
  --paper: #f3f5f8;
  --muted: #6b7280;
  --line: #dbe1e9;
  --teal: #159a92;
  --teal-dark: #0f756f;
  --blue: #2d67e8;
  --blue-dark: #1f4fbd;
  --orange: #f27b2b;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
  background: #dfe4ea;
}

body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family:
    "Microsoft YaHei", "PingFang SC", "Noto Sans CJK SC", Arial, sans-serif;
}

button,
input {
  font: inherit;
}

button {
  -webkit-tap-highlight-color: transparent;
}

.site-shell {
  width: min(100%, 920px);
  min-height: 100vh;
  margin: 0 auto;
  padding-bottom: 86px;
  background: #fff;
  box-shadow: 0 0 40px rgb(15 23 42 / 10%);
}

.site-header {
  padding: 28px 22px 22px;
  color: #fff;
  text-align: center;
  background:
    linear-gradient(135deg, rgb(17 23 34 / 96%), rgb(17 23 34 / 86%)),
    radial-gradient(circle at top right, var(--orange), transparent 42%);
  border-bottom: 6px solid var(--orange);
}

.site-header h1 {
  margin: 6px 0 8px;
  font-family: Georgia, "Songti SC", serif;
  font-size: clamp(30px, 8vw, 48px);
  line-height: 1.15;
  letter-spacing: 0.02em;
}

.eyebrow {
  margin: 0;
  color: #ffbf8f;
  font-size: 12px;
  font-weight: 800;
  letter-spacing: 0.16em;
}

.header-note {
  margin: 0;
  color: #dbe4f0;
  font-size: 14px;
}

.home-panel,
.content-panel {
  padding: 20px 16px 34px;
}

.intro-card {
  padding: 24px 22px;
  margin-bottom: 16px;
  background: #fff8f2;
  border: 1px solid #ffd6b8;
  border-radius: 18px;
}

.intro-kicker {
  color: #bf5311;
  font-size: 12px;
  font-weight: 800;
  letter-spacing: 0.14em;
}

.intro-card h2 {
  margin: 8px 0;
  font-size: 25px;
}

.intro-card p {
  margin: 0;
  color: #5f6570;
  line-height: 1.65;
}

.section-card {
  width: 100%;
  min-height: 104px;
  display: grid;
  grid-template-columns: auto 1fr auto;
  gap: 16px;
  align-items: center;
  margin: 14px 0;
  padding: 18px;
  color: #fff;
  text-align: left;
  border: 0;
  border-radius: 18px;
  cursor: pointer;
  box-shadow: 0 12px 22px rgb(15 23 42 / 14%);
  transition:
    transform 160ms ease,
    box-shadow 160ms ease;
}

.section-card:active {
  transform: scale(0.985);
}

.section-card.teal {
  background: linear-gradient(135deg, var(--teal-dark), var(--teal));
}

.section-card.blue {
  background: linear-gradient(135deg, var(--blue-dark), var(--blue));
}

.section-number {
  display: grid;
  width: 50px;
  height: 50px;
  place-items: center;
  border: 1px solid rgb(255 255 255 / 42%);
  border-radius: 50%;
  font-family: Georgia, serif;
  font-size: 19px;
  font-weight: 700;
}

.section-copy {
  display: grid;
  gap: 5px;
}

.section-copy strong {
  font-family: Georgia, "Songti SC", serif;
  font-size: 22px;
}

.section-copy small {
  color: rgb(255 255 255 / 78%);
  font-size: 13px;
}

.section-arrow {
  font-size: 28px;
}

.free-note {
  display: flex;
  gap: 9px;
  align-items: center;
  padding: 14px 4px 0;
  color: var(--muted);
  font-size: 13px;
  line-height: 1.5;
}

.free-note span {
  color: #22a86b;
  font-size: 10px;
}

.section-heading {
  display: flex;
  gap: 15px;
  align-items: flex-end;
  justify-content: space-between;
  padding-bottom: 17px;
  border-bottom: 1px solid var(--line);
}

.section-heading button {
  padding: 9px 12px;
  color: #435166;
  background: #eef2f7;
  border: 0;
  border-radius: 999px;
  cursor: pointer;
}

.section-heading div {
  text-align: right;
}

.section-heading p {
  margin: 0 0 4px;
  color: var(--muted);
  font-size: 12px;
}

.section-heading h2 {
  margin: 0;
  font-family: Georgia, "Songti SC", serif;
  font-size: clamp(24px, 7vw, 36px);
}

.mechanism-list,
.reference-grid {
  display: grid;
  gap: 18px;
  margin-top: 18px;
}

.mechanism-card {
  overflow: hidden;
  background: #f7f8fa;
  border: 1px solid var(--line);
  border-radius: 18px;
  box-shadow: 0 8px 18px rgb(15 23 42 / 7%);
}

.mechanism-title {
  display: flex;
  gap: 12px;
  align-items: center;
  padding: 15px 17px;
  color: #fff;
  background: var(--ink);
}

.mechanism-title span {
  color: #ff9a54;
  font-family: Georgia, serif;
  font-size: 19px;
}

.mechanism-title h3 {
  margin: 0;
  font-size: 20px;
}

.video-pair {
  display: grid;
  gap: 1px;
  background: var(--line);
}

.video-card {
  overflow: hidden;
  background: #f7f8fb;
}

.video-label {
  padding: 9px 12px;
  color: #fff;
  text-align: center;
  font-size: 14px;
  font-weight: 800;
}

.video-card.teal .video-label,
.video-card.teal .play-button {
  background: var(--teal);
}

.video-card.blue .video-label,
.video-card.blue .play-button {
  background: var(--blue);
}

.poster-button {
  position: relative;
  width: 100%;
  min-height: 320px;
  display: grid;
  place-items: center;
  padding: 18px;
  background: #171c25;
  border: 0;
  cursor: pointer;
}

.poster-button img {
  width: 100%;
  height: 360px;
  object-fit: contain;
}

.poster-play {
  position: absolute;
  inset: 50% auto auto 50%;
  width: 72px;
  height: 72px;
  display: grid;
  place-items: center;
  transform: translate(-50%, -50%);
  background: rgb(17 23 34 / 76%);
  border: 4px solid #fff;
  border-radius: 50%;
  box-shadow: 0 8px 24px rgb(0 0 0 / 32%);
}

.play-triangle {
  width: 0;
  height: 0;
  margin-left: 4px;
  border-top: 9px solid transparent;
  border-bottom: 9px solid transparent;
  border-left: 15px solid currentColor;
}

.video-player {
  width: 100%;
  min-height: 320px;
  max-height: 72vh;
  display: block;
  background: #0c1017;
  border: 0;
  object-fit: contain;
}

.native-player {
  background: #0c1017;
}

.video-stage {
  position: relative;
  min-height: 320px;
  display: grid;
  place-items: center;
  background: #0c1017;
}

.player-status {
  position: absolute;
  inset: auto 12px 12px;
  padding: 8px 12px;
  color: #fff;
  text-align: center;
  background: rgb(17 23 34 / 76%);
  border-radius: 999px;
  font-size: 13px;
  pointer-events: none;
}

.player-status:empty,
.player-status[hidden] {
  display: none;
}

.player-controls {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr) auto auto;
  gap: 10px;
  align-items: center;
  min-height: 70px;
  padding: 10px 12px;
  color: #fff;
}

.player-controls.teal {
  background: var(--teal);
}

.player-controls.blue {
  background: var(--blue);
}

.control-button {
  min-width: 52px;
  min-height: 48px;
  display: grid;
  gap: 2px;
  place-content: center;
  padding: 5px 9px;
  color: #fff;
  background: rgb(0 0 0 / 15%);
  border: 1px solid rgb(255 255 255 / 22%);
  border-radius: 10px;
  cursor: pointer;
  font-size: 11px;
  font-weight: 800;
}

.control-main {
  min-width: 64px;
}

.control-icon {
  min-height: 18px;
  font-size: 18px;
  line-height: 1;
}

.progress-group {
  min-width: 0;
  display: grid;
  gap: 4px;
}

.player-progress {
  width: 100%;
  height: 26px;
  margin: 0;
  accent-color: #fff;
  cursor: pointer;
}

.player-time {
  display: flex;
  gap: 4px;
  justify-content: center;
  color: rgb(255 255 255 / 88%);
  font-variant-numeric: tabular-nums;
  font-size: 11px;
}

.native-player:fullscreen {
  display: grid;
  grid-template-rows: minmax(0, 1fr) auto;
  width: 100vw;
  height: 100vh;
  background: #000;
}

.native-player:fullscreen .video-stage,
.native-player:fullscreen .video-player {
  width: 100%;
  height: 100%;
  max-height: none;
}

.play-button {
  width: 100%;
  min-height: 52px;
  display: flex;
  gap: 10px;
  align-items: center;
  justify-content: center;
  color: #fff;
  border: 0;
  cursor: pointer;
  font-size: 16px;
  font-weight: 800;
}

.play-button .play-triangle {
  border-top-width: 6px;
  border-bottom-width: 6px;
  border-left-width: 10px;
}

.search-field {
  display: grid;
  gap: 7px;
  margin: 18px 0 2px;
  color: #4b5563;
  font-size: 13px;
  font-weight: 700;
}

.search-field input {
  width: 100%;
  height: 48px;
  padding: 0 15px;
  color: var(--ink);
  background: #f7f8fa;
  border: 1px solid #cfd6e1;
  border-radius: 12px;
  outline: none;
}

.search-field input:focus {
  border-color: var(--blue);
  box-shadow: 0 0 0 3px rgb(45 103 232 / 14%);
}

.reference-grid .video-card {
  border: 1px solid var(--line);
  border-radius: 16px;
  box-shadow: 0 7px 16px rgb(15 23 42 / 7%);
}

.bottom-nav {
  position: fixed;
  z-index: 30;
  inset: auto 0 0;
  width: min(100%, 920px);
  height: 70px;
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  margin: 0 auto;
  background: rgb(255 255 255 / 94%);
  border-top: 1px solid #d5dbe5;
  box-shadow: 0 -9px 25px rgb(15 23 42 / 10%);
  backdrop-filter: blur(14px);
}

.bottom-nav button {
  display: grid;
  gap: 3px;
  place-content: center;
  color: #778194;
  background: transparent;
  border: 0;
  cursor: pointer;
  font-size: 11px;
}

.bottom-nav button span {
  font-size: 19px;
}

.bottom-nav button.active {
  color: var(--blue);
  font-weight: 800;
}

@media (min-width: 720px) {
  .home-panel,
  .content-panel {
    padding: 28px 30px 42px;
  }

  .video-pair,
  .reference-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .poster-button img {
    height: 390px;
  }
}

@media (max-width: 420px) {
  .site-header {
    padding-inline: 16px;
  }

  .home-panel,
  .content-panel {
    padding-inline: 12px;
  }

  .section-card {
    gap: 12px;
    padding-inline: 14px;
  }

  .section-number {
    width: 44px;
    height: 44px;
  }

  .section-copy strong {
    font-size: 19px;
  }

  .poster-button {
    min-height: 290px;
    padding: 12px;
  }

  .poster-button img {
    height: 330px;
  }

  .player-controls {
    grid-template-columns: auto minmax(90px, 1fr) auto auto;
    gap: 6px;
    padding-inline: 8px;
  }

  .control-button {
    min-width: 46px;
    padding-inline: 6px;
  }

  .control-main {
    min-width: 54px;
  }

  .control-button span:last-child {
    font-size: 10px;
  }
}

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