* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  min-width: 320px;
  font-family: ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
  font-size: 16px;
  letter-spacing: 0;
  line-height: 1.65;
}

a {
  color: inherit;
  text-decoration: none;
}

img,
svg {
  display: block;
}

h1,
h2,
h3,
p {
  margin-top: 0;
}

h1,
h2,
h3 {
  color: var(--dt-navy);
  letter-spacing: 0;
}

.container {
  margin-inline: auto;
  width: min(var(--container), calc(100% - 40px));
}

.skip-link {
  background: var(--dt-navy);
  border-radius: 8px;
  color: #fff;
  left: 12px;
  padding: 10px 14px;
  position: fixed;
  top: 12px;
  transform: translateY(-150%);
  z-index: 1000;
}

.skip-link:focus {
  transform: translateY(0);
}

.site-header {
  backdrop-filter: blur(16px);
  position: sticky;
  top: 0;
  z-index: 100;
}

.header-inner {
  align-items: center;
  display: flex;
  gap: 22px;
  justify-content: space-between;
}

.brand,
.footer-brand {
  align-items: center;
  display: inline-flex;
  gap: 11px;
}

.brand strong,
.brand small,
.footer-logo {
  display: block;
}

.brand strong,
.footer-logo {
  line-height: 1.15;
  margin: 0;
}

.brand small {
  color: var(--dt-muted);
  font-size: 12px;
}

.desktop-nav,
.header-actions {
  align-items: center;
  display: flex;
}

.desktop-nav a,
.mobile-nav a {
  align-items: center;
  display: inline-flex;
  font-size: 14px;
  min-height: 44px;
  padding: 10px 13px;
}

.btn,
.header-download {
  align-items: center;
  display: inline-flex;
  gap: 9px;
  justify-content: center;
}

.icon-button {
  display: inline-grid;
  height: 44px;
  place-items: center;
  width: 44px;
}

.mobile-menu-button,
.mobile-nav {
  display: none;
}

.site-footer {
  background: #fff;
  border-top: 1px solid var(--dt-line);
  padding: 34px 0;
}

.footer-grid {
  align-items: start;
  display: grid;
  gap: 42px;
  grid-template-columns: minmax(0, 1fr) auto minmax(240px, .7fr);
}

.site-footer nav {
  color: var(--dt-blue-700);
  display: grid;
  font-weight: 750;
  gap: 10px;
}

.footer-text,
.footer-note {
  color: var(--dt-muted);
}

.footer-note p,
.footer-text {
  margin-bottom: 6px;
}

.expanded-article-section {
  background: #f5f8ff;
  border-top: 1px solid var(--dt-line);
  padding: 66px 0 80px;
}

.expanded-article-head {
  align-items: end;
  display: flex;
  gap: 26px;
  justify-content: space-between;
  margin-bottom: 32px;
}

.expanded-article-head h2 {
  font-size: 36px;
  margin-bottom: 8px;
}

.expanded-article-head p {
  color: var(--dt-muted);
  margin: 0;
  max-width: 600px;
}

.expanded-article-count {
  background: #fff;
  border: 1px solid var(--dt-line);
  border-radius: 8px;
  color: var(--dt-blue-700);
  flex: none;
  font-weight: 800;
  padding: 10px 14px;
}

.expanded-article-grid {
  display: grid;
  gap: 18px;
  grid-template-columns: repeat(3, minmax(0, 1fr));
}

.expanded-card {
  background: #fff;
  border: 1px solid var(--dt-line);
  border-radius: 8px;
  display: flex;
  flex-direction: column;
  min-height: 410px;
  overflow: hidden;
  transition: border-color .16s ease, box-shadow .16s ease, transform .16s ease;
}

.expanded-card:hover {
  border-color: #bfd7ff;
  box-shadow: 0 18px 38px rgba(22, 119, 255, .12);
  transform: translateY(-2px);
}

.expanded-card img {
  aspect-ratio: 16 / 10;
  background: #eef5ff;
  object-fit: cover;
  width: 100%;
}

.expanded-card-content {
  display: flex;
  flex: 1;
  flex-direction: column;
  padding: 18px 18px 20px;
}

.expanded-card-content span {
  color: var(--dt-blue-700);
  font-size: 13px;
  font-weight: 850;
}

.expanded-card-content h3 {
  font-size: 20px;
  line-height: 1.38;
  margin: 8px 0 10px;
}

.expanded-card-content p {
  color: var(--dt-muted);
  font-size: 14px;
  line-height: 1.68;
  margin-bottom: 18px;
}

.expanded-card-content em {
  color: var(--dt-blue-700);
  font-style: normal;
  font-weight: 800;
  margin-top: auto;
}

.library-article-hero {
  background: linear-gradient(180deg, #eff6ff, #fff);
  border-bottom: 1px solid var(--dt-line);
  padding: 54px 0 44px;
}

.library-back-link {
  align-items: center;
  color: var(--dt-blue-700);
  display: inline-flex;
  font-weight: 800;
  gap: 8px;
  margin-bottom: 26px;
  min-height: 42px;
}

.library-back-link svg {
  height: 18px;
  width: 18px;
}

.library-hero-grid {
  align-items: center;
  display: grid;
  gap: 40px;
  grid-template-columns: minmax(0, .94fr) minmax(360px, .88fr);
}

.library-kicker {
  color: var(--dt-blue-700);
  font-size: 14px;
  font-weight: 850;
  margin: 0 0 12px;
}

.library-title {
  font-size: clamp(38px, 5vw, 54px);
  line-height: 1.16;
  margin-bottom: 18px;
}

.library-summary {
  color: var(--dt-muted);
  font-size: 18px;
  line-height: 1.76;
  margin-bottom: 20px;
}

.library-meta {
  color: #536381;
  display: flex;
  flex-wrap: wrap;
  font-size: 14px;
  font-weight: 700;
  gap: 18px;
}

.library-cover {
  background: #fff;
  border: 1px solid var(--dt-line);
  border-radius: 8px;
  box-shadow: 0 22px 56px rgba(18, 60, 122, .12);
  margin: 0;
  overflow: hidden;
  padding: 10px;
}

.library-cover img {
  aspect-ratio: 16 / 10;
  background: #eef5ff;
  border-radius: 6px;
  object-fit: cover;
  width: 100%;
}

.library-cover figcaption {
  color: var(--dt-muted);
  font-size: 13px;
  padding: 10px 6px 4px;
}

.library-body {
  padding: 54px 0 82px;
}

.library-body-grid {
  align-items: start;
  display: grid;
  gap: 42px;
  grid-template-columns: 220px minmax(0, 700px);
  justify-content: center;
}

.library-outline {
  border-left: 2px solid #d5e4ff;
  display: grid;
  gap: 12px;
  padding-left: 16px;
  position: sticky;
  top: 96px;
}

.library-outline strong {
  color: var(--dt-navy);
  font-size: 14px;
}

.library-outline a {
  color: var(--dt-muted);
  font-size: 14px;
  line-height: 1.48;
}

.library-outline a:hover {
  color: var(--dt-blue-700);
}

.library-prose section + section {
  border-top: 1px solid #e7effc;
  margin-top: 38px;
  padding-top: 38px;
}

.library-prose h2 {
  font-size: 30px;
  margin-bottom: 14px;
}

.library-prose p,
.library-prose li {
  color: #37445f;
  font-size: 17px;
  line-height: 1.88;
}

.library-prose ul {
  display: grid;
  gap: 8px;
  margin: 16px 0 0;
  padding-left: 22px;
}

.library-note {
  background: #eff6ff;
  border-left: 3px solid var(--dt-blue);
  border-radius: 6px;
  color: #344563;
  margin-bottom: 36px;
  padding: 18px 20px;
}

.library-note strong {
  color: var(--dt-navy);
  display: block;
  margin-bottom: 4px;
}

@media (max-width: 980px) {
  .desktop-nav {
    display: none;
  }

  .mobile-menu-button {
    display: inline-grid;
  }

  .mobile-nav {
    background: #fff;
    border: 1px solid var(--dt-line);
    border-radius: 8px;
    box-shadow: 0 18px 45px rgba(31, 42, 68, .14);
    margin: 0 auto 14px;
    padding: 8px;
    width: min(var(--container), calc(100% - 40px));
  }

  .mobile-nav.open {
    display: grid;
  }

  .footer-grid {
    grid-template-columns: 1fr;
  }

  .expanded-article-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .library-hero-grid,
  .library-body-grid {
    grid-template-columns: 1fr;
  }

  .library-outline {
    display: none;
  }
}

@media (max-width: 680px) {
  .container {
    width: min(var(--container), calc(100% - 28px));
  }

  .brand small,
  .header-download {
    display: none;
  }

  .expanded-article-section {
    padding: 46px 0 56px;
  }

  .expanded-article-head {
    align-items: start;
    flex-direction: column;
    margin-bottom: 24px;
  }

  .expanded-article-grid {
    grid-template-columns: 1fr;
  }

  .expanded-card {
    min-height: 0;
  }

  .library-article-hero {
    padding: 36px 0;
  }

  .library-title {
    font-size: 36px;
  }

  .library-body {
    padding: 38px 0 54px;
  }

  .library-prose h2 {
    font-size: 26px;
  }
}