:root {
  color-scheme: light;
  --bg: #f4f7fb;
  --surface: #ffffff;
  --surface-soft: #e8f1ff;
  --text: #273142;
  --muted: #697487;
  --line: #dbe5f1;
  --accent: #2563eb;
  --accent-strong: #1d4ed8;
  --accent-soft: #dbeafe;
  --button-text: #ffffff;
  --sidebar: #eef3f9;
  --sidebar-text: #2d3748;
  --sidebar-muted: #687386;
  --sidebar-line: #dde6f0;
  --sidebar-active: #dbeafe;
  --sidebar-width: 260px;
}

:root[data-theme="dark"] {
  color-scheme: dark;
  --bg: #101827;
  --surface: #182235;
  --surface-soft: #20304a;
  --text: #e6edf7;
  --muted: #a7b3c6;
  --line: #28364f;
  --accent: #7db6ff;
  --accent-strong: #9cc8ff;
  --accent-soft: #1f3558;
  --button-text: #07111f;
  --sidebar: #0c1422;
  --sidebar-text: #e6edf7;
  --sidebar-muted: #9aa8bc;
  --sidebar-line: #1d2a3e;
  --sidebar-active: #172842;
}

* {
  box-sizing: border-box;
}

html {
  background: var(--bg);
  color: var(--text);
  font-family: "Inter", "Noto Sans SC", "Microsoft YaHei", system-ui, -apple-system, sans-serif;
  font-size: 16px;
  letter-spacing: 0;
}

body {
  margin: 0;
  min-height: 100vh;
  background: var(--bg);
  color: var(--text);
  line-height: 1.75;
}

a {
  color: var(--accent-strong);
  text-decoration: none;
}

a:hover {
  color: var(--accent);
}

.site-shell {
  width: min(1120px, calc(100% - 40px));
  margin: 0 auto;
}

.site-header {
  background: var(--sidebar);
  border-right: 1px solid var(--sidebar-line);
  bottom: 0;
  color: var(--sidebar-text);
  left: 0;
  padding: 32px 24px;
  position: fixed;
  top: 0;
  width: var(--sidebar-width);
  z-index: 10;
}

.site-header .site-shell {
  margin: 0;
  width: auto;
}

.nav {
  display: flex;
  align-items: stretch;
  flex-direction: column;
  gap: 32px;
  height: 100%;
  justify-content: flex-start;
}

.brand {
  display: inline-flex;
  flex-direction: column;
  gap: 6px;
  color: var(--sidebar-text);
  padding-bottom: 14px;
  border-bottom: 1px solid var(--sidebar-line);
}

.avatar {
  background: var(--surface);
  border: 1px solid var(--sidebar-line);
  border-radius: 50%;
  display: block;
  height: 88px;
  margin-bottom: 10px;
  object-fit: cover;
  width: 88px;
}

.brand-title {
  font-size: 1.48rem;
  font-weight: 850;
  letter-spacing: 0;
}

.brand-subtitle {
  color: var(--sidebar-muted);
  font-size: 0.8rem;
  line-height: 1.5;
}

.profile-note {
  border-bottom: 1px solid var(--sidebar-line);
  color: var(--sidebar-muted);
  font-size: 0.84rem;
  line-height: 1.65;
  margin: -18px 0 0;
  padding: 0 0 22px;
}

.nav-links {
  display: flex;
  flex-direction: column;
  gap: 4px;
  justify-content: flex-start;
}

.nav-links a {
  border-radius: 10px;
  color: var(--sidebar-muted);
  font-size: 0.95rem;
  font-weight: 600;
  padding: 9px 12px;
}

.nav-links a:hover,
.nav-links a[aria-current="page"] {
  background: var(--sidebar-active);
  color: var(--accent-strong);
}

.theme-toggle {
  align-items: center;
  background: transparent;
  border: 1px solid var(--sidebar-line);
  border-radius: 10px;
  color: var(--sidebar-muted);
  cursor: pointer;
  display: inline-flex;
  font: inherit;
  font-size: 0.9rem;
  font-weight: 650;
  gap: 8px;
  justify-content: center;
  margin-top: auto;
  min-height: 38px;
  padding: 8px 12px;
  width: 100%;
}

.theme-toggle:hover {
  background: var(--sidebar-active);
  color: var(--accent-strong);
}

.theme-toggle-icon {
  font-size: 1rem;
  line-height: 1;
}

.text-link {
  color: var(--accent-strong);
  font-size: 0.94rem;
  padding: 0;
}

.text-link:hover {
  color: var(--accent);
}

body > main.site-shell,
.site-footer .site-shell {
  margin-left: calc(var(--sidebar-width) + 44px);
  margin-right: 44px;
  max-width: 1180px;
  width: auto;
}

.hero {
  display: grid;
  grid-template-columns: minmax(0, 1.25fr) minmax(280px, 0.75fr);
  gap: 24px;
  padding: 38px 0 24px;
  align-items: end;
}

.eyebrow {
  color: var(--accent);
  font-size: 0.86rem;
  font-weight: 700;
  letter-spacing: 0;
  margin: 0 0 10px;
}

.hero h1 {
  font-family: "Inter", "Noto Sans SC", "Microsoft YaHei", system-ui, -apple-system, sans-serif;
  font-size: clamp(2rem, 3.8vw, 3.1rem);
  font-weight: 760;
  line-height: 1.12;
  letter-spacing: 0;
  margin: 0;
}

.hero-copy {
  color: var(--muted);
  font-size: 1.02rem;
  margin: 24px 0 0;
  max-width: 680px;
}

.hero-panel {
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 10px;
  padding: 18px;
}

.hero-panel p {
  margin: 0 0 14px;
}

.quick-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  margin-top: 20px;
}

.button {
  align-items: center;
  background: var(--accent);
  border: 1px solid var(--accent);
  border-radius: 8px;
  color: var(--button-text);
  display: inline-flex;
  font-weight: 700;
  min-height: 40px;
  padding: 8px 14px;
}

.button:hover {
  background: var(--accent-strong);
  border-color: var(--accent-strong);
  color: var(--button-text);
}

.button.secondary {
  background: transparent;
  border-color: var(--line);
  color: var(--text);
}

.button.secondary:hover {
  background: var(--surface-soft);
  border-color: var(--accent);
  color: var(--accent);
}

.section {
  padding: 20px 0;
}

.section-header {
  align-items: end;
  border-top: 0;
  display: flex;
  gap: 20px;
  justify-content: space-between;
  padding-top: 8px;
}

.section h2 {
  font-family: "Inter", "Noto Sans SC", "Microsoft YaHei", system-ui, -apple-system, sans-serif;
  font-size: clamp(1.25rem, 2.2vw, 1.65rem);
  font-weight: 720;
  line-height: 1.2;
  margin: 0;
}

.section-note {
  color: var(--muted);
  margin: 8px 0 0;
  max-width: 680px;
}

.course-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 12px;
  margin-top: 18px;
}

.course-group,
.friend-card,
.plain-card {
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 10px;
}

.course-group {
  padding: 18px;
}

.course-group h3 {
  color: var(--text);
  font-size: 1rem;
  margin: 0 0 12px;
}

.link-list {
  display: grid;
  gap: 8px;
  margin: 0;
  padding: 0;
  list-style: none;
}

.link-list a {
  align-items: center;
  border-radius: 8px;
  color: var(--text);
  display: flex;
  justify-content: space-between;
  padding: 7px 8px;
}

.link-list a::after {
  color: var(--muted);
  content: "↗";
  font-size: 0.82rem;
}

.link-list a:hover {
  background: var(--surface-soft);
  color: var(--accent);
}

.tool-row {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 12px;
  margin-top: 18px;
}

.plain-card {
  min-height: 112px;
  padding: 16px;
}

.plain-card h3 {
  color: var(--text);
  margin: 0 0 8px;
  font-size: 1rem;
}

.plain-card p {
  color: var(--muted);
  font-size: 0.94rem;
  margin: 0;
}

.friend-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 12px;
  margin-top: 18px;
}

.friend-card {
  min-height: 136px;
  padding: 16px;
}

.friend-card .meta {
  color: var(--accent);
  font-size: 0.82rem;
  font-weight: 700;
  margin: 0 0 8px;
}

.friend-card h3 {
  font-size: 1.08rem;
  margin: 0 0 8px;
}

.friend-card p {
  color: var(--muted);
  font-size: 0.94rem;
  margin: 0 0 14px;
}

.friend-card.placeholder {
  background: transparent;
  border-style: dashed;
}

.site-footer {
  border-top: 1px solid var(--line);
  color: var(--muted);
  font-size: 0.9rem;
  margin-top: 36px;
  padding: 24px 0 36px;
}

.footer-inner {
  display: flex;
  justify-content: space-between;
  gap: 20px;
}

.not-found {
  display: grid;
  min-height: 70vh;
  place-items: center;
  text-align: center;
}

.not-found h1 {
  font-family: "Inter", "Noto Sans SC", "Microsoft YaHei", system-ui, -apple-system, sans-serif;
  font-size: clamp(3rem, 12vw, 7rem);
  font-weight: 800;
  line-height: 1;
  margin: 0 0 12px;
}

@media (max-width: 860px) {
  .site-header {
    background: var(--surface);
    border-bottom: 1px solid var(--line);
    border-right: 0;
    color: var(--text);
    padding: 18px 0 14px;
    position: static;
    width: auto;
  }

  .site-header .site-shell {
    margin: 0 auto;
    width: min(1120px, calc(100% - 40px));
  }

  .nav {
    align-items: center;
    flex-direction: row;
    gap: 20px;
    height: auto;
    justify-content: space-between;
  }

  .brand {
    border-bottom: 0;
    color: var(--text);
    gap: 2px;
    padding-bottom: 0;
  }

  .avatar {
    height: 42px;
    margin-bottom: 4px;
    width: 42px;
  }

  .brand-title {
    font-size: 1.05rem;
  }

  .brand-subtitle {
    color: var(--muted);
  }

  .profile-note {
    display: none;
  }

  .nav-links {
    flex-direction: row;
    flex-wrap: wrap;
    justify-content: flex-end;
  }

  .nav-links a {
    color: var(--muted);
    padding: 4px 6px;
  }

  .nav-links a:hover,
  .nav-links a[aria-current="page"] {
    background: transparent;
    color: var(--accent);
  }

  .theme-toggle {
    border-color: var(--line);
    color: var(--muted);
    margin-top: 0;
    min-height: 34px;
    padding: 5px 9px;
    width: auto;
  }

  .theme-toggle:hover {
    background: transparent;
    color: var(--accent);
  }

  body > main.site-shell,
  .site-footer .site-shell {
    margin-left: auto;
    margin-right: auto;
    width: min(1120px, calc(100% - 40px));
  }

  .hero,
  .course-grid,
  .tool-row,
  .friend-grid {
    grid-template-columns: 1fr;
  }

  .hero {
    align-items: start;
    padding-top: 38px;
  }

  .hero-panel {
    border-left: 0;
    border-top: 1px solid var(--line);
    padding: 18px;
  }
}

@media (max-width: 620px) {
  .site-shell {
    width: min(100% - 24px, 1120px);
  }

  .nav,
  .section-header,
  .footer-inner {
    align-items: flex-start;
    flex-direction: column;
  }

  .nav-links {
    justify-content: flex-start;
  }
}