/* ============================================================
   Xiang Li — Personal Academic Homepage
   Mathematical Modernist design
   ============================================================ */

/* === CSS Reset === */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
img { display: block; max-width: 100%; }

/* === Custom Properties === */
:root {
  --font-serif: 'Cormorant Garamond', Georgia, 'Times New Roman', serif;
  --font-sans: 'Inter', system-ui, -apple-system, sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', monospace;

  --bg: #faf8f5;
  --text: #1a1a2e;
  --text-secondary: #5a6070;
  --text-muted: #8a8a8a;
  --accent: #b0852b;
  --accent-soft: #d4b96a;
  --theorem-bg: #f4f1eb;
  --theorem-border: #c9a84c;
  --aside-bg: #f6f4f0;
  --aside-border: #c0bbb0;
  --card-bg: #ffffff;
  --card-border: #e8e4dc;
  --nav-bg: rgba(250, 248, 245, 0.9);
  --nav-shadow: rgba(0,0,0,0.04);
  --border: #e0dcd5;
  --tag-bg: #eeebe4;
  --tag-text: #6a6558;
  --link: #4a6d8a;
  --link-hover: #2c4a6a;
  --surface: #ffffff;
}

[data-theme="dark"] {
  --bg: #151922;
  --text: #e8e4dd;
  --text-secondary: #9ca3b0;
  --text-muted: #6a6e78;
  --accent: #c9a84c;
  --accent-soft: #a08840;
  --theorem-bg: #1c2030;
  --theorem-border: #c9a84c;
  --aside-bg: #1a1e2a;
  --aside-border: #4a4d55;
  --card-bg: #1e2332;
  --card-border: #2a3040;
  --nav-bg: rgba(21, 25, 34, 0.9);
  --nav-shadow: rgba(0,0,0,0.2);
  --border: #2a3040;
  --tag-bg: #252a38;
  --tag-text: #9ca3b0;
  --link: #8aabda;
  --link-hover: #aac4ee;
  --surface: #1a1e2a;
}

/* === Base / Typography === */
html { scroll-behavior: smooth; scroll-padding-top: 4rem; }

body {
  font-family: var(--font-sans);
  font-size: 16px;
  line-height: 1.65;
  color: var(--text);
  background: var(--bg);
  transition: background-color 0.3s ease, color 0.3s ease;
  -webkit-font-smoothing: antialiased;
}

h1, h2, h3, h4 { font-family: var(--font-serif); font-weight: 600; line-height: 1.25; }
h2 { font-size: 1.75rem; color: var(--text); margin-bottom: 2rem; letter-spacing: -0.01em; }

a { color: var(--link); text-decoration: none; transition: color 0.2s; }
a:hover { color: var(--link-hover); text-decoration: underline; }

strong { font-weight: 600; color: var(--text); }
code { font-family: var(--font-mono); font-size: 0.9em; background: var(--tag-bg); padding: 0.15em 0.4em; border-radius: 3px; }
p { margin-bottom: 1rem; }
p:last-child { margin-bottom: 0; }

::selection { background: var(--accent-soft); color: #fff; }

/* === Layout === */
.container { max-width: 720px; margin: 0 auto; padding: 0 clamp(1rem, 4vw, 2rem); }
.section { padding: 5rem 0; }
.section__heading {
  font-family: var(--font-serif);
  font-size: 1.75rem;
  font-weight: 600;
  display: flex;
  align-items: center;
  gap: 0.75rem;
}
.section__heading::after {
  content: '';
  flex: 1;
  height: 1px;
  background: var(--theorem-border);
  opacity: 0.4;
}

/* === Navigation === */
.nav {
  position: sticky; top: 0; z-index: 100;
  background: var(--nav-bg);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--card-border);
  padding: 0.6rem 0;
  transition: background-color 0.3s ease, border-color 0.3s ease;
}
.nav__inner {
  max-width: 720px;
  margin: 0 auto;
  padding: 0 clamp(1rem, 4vw, 2rem);
  display: flex; align-items: center; justify-content: space-between;
}
.nav__name {
  font-family: var(--font-serif);
  font-size: 1.15rem;
  font-weight: 600;
  color: var(--text);
  text-decoration: none;
}
.nav__name:hover { color: var(--accent); text-decoration: none; }
.nav__links { display: flex; gap: 1.25rem; list-style: none; align-items: center; flex-wrap: wrap; }
.nav__links a {
  font-size: 0.85rem;
  font-weight: 500;
  color: var(--text-secondary);
  text-decoration: none;
  letter-spacing: 0.02em;
  transition: color 0.2s;
}
.nav__links a:hover, .nav__links a.active { color: var(--accent); text-decoration: none; }

#theme-toggle {
  background: none; border: 1px solid var(--card-border); border-radius: 50%;
  width: 34px; height: 34px;
  display: flex; align-items: center; justify-content: center;
  cursor: pointer;
  font-size: 1rem;
  color: var(--text-secondary);
  transition: background-color 0.2s, color 0.2s, border-color 0.2s;
  line-height: 1;
}
#theme-toggle:hover { background: var(--tag-bg); color: var(--text); }

/* === Hero === */
.hero {
  padding: clamp(2.5rem, 6vw, 4rem) 0 2rem;
  text-align: center;
  position: relative;
  isolation: isolate;
}
.hero::before {
  content: '';
  position: absolute;
  inset: 0;
  background: url('external/images/X13.jpg') center/contain no-repeat;
  opacity: 0.10;
  z-index: -1;
}
[data-theme="dark"] .hero::before { opacity: 0.08; }

.hero__name {
  font-family: var(--font-serif);
  font-size: clamp(2rem, 5vw, 3rem);
  font-weight: 700;
  color: var(--text);
  letter-spacing: -0.02em;
}
.hero__name-cn {
  font-family: var(--font-sans);
  font-size: 1.15rem;
  color: var(--text-secondary);
  margin-top: 0.2rem;
  font-weight: 400;
}
.hero__subtitle {
  font-size: 1rem;
  color: var(--text-secondary);
  margin-top: 0.75rem;
  font-weight: 400;
}
.hero__affiliation {
  font-size: 0.9rem;
  color: var(--text-muted);
  margin-top: 0.3rem;
}
.hero__contact {
  font-size: 0.9rem;
  color: var(--text-muted);
  margin-top: 0.5rem;
}
.hero__contact a {
  color: var(--link);
  font-weight: 500;
}

/* === Theorem Blocks (signature feature) === */
.theorem {
  margin: 1.75rem 0;
  padding: 1.25rem 1.5rem 1.25rem 1.75rem;
  border-left: 3px solid var(--theorem-border);
  background: var(--theorem-bg);
  border-radius: 0 6px 6px 0;
  transition: background-color 0.3s ease;
}
.theorem-heading {
  font-family: var(--font-sans);
  font-size: 0.85rem;
  font-weight: 600;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--accent);
  margin-bottom: 0.75rem;
}
.theorem-heading__number { opacity: 0.7; margin-left: 0.3em; font-weight: 500; }
.theorem-body { color: var(--text); }

/* Aside variant — softer, dashed left border */
.theorem--aside {
  border-left-style: dashed;
  border-left-color: var(--aside-border);
  background: var(--aside-bg);
  font-size: 0.95rem;
  color: var(--text-secondary);
  font-style: italic;
}
.theorem--aside .theorem-heading { color: var(--text-muted); font-weight: 500; }

/* Proof variant — smaller heading, subtle */
.theorem--proof .theorem-heading { font-size: 0.8rem; color: var(--text-muted); }
.theorem--proof .theorem-body { font-style: italic; }

/* Figure */
.theorem-figure { margin: 2rem 0; text-align: center; }
.theorem-figure__image {
  max-width: 55%;
  margin: 0 auto;
  border-radius: 4px;
  box-shadow: 0 2px 12px rgba(0,0,0,0.08);
}
.theorem-figure__caption {
  margin-top: 0.75rem;
  font-size: 0.9rem;
  color: var(--text-muted);
  font-style: italic;
}
.theorem-figure__caption-type { font-weight: 600; font-style: normal; }

/* === Timeline (CV) === */
.timeline { list-style: none; display: flex; flex-direction: column; gap: 1.5rem; }
.timeline__item {
  display: grid;
  grid-template-columns: 160px 1fr;
  gap: 1.25rem;
  align-items: start;
}
.timeline__date {
  font-family: var(--font-sans);
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--accent);
  text-align: right;
  padding-top: 0.15rem;
  letter-spacing: 0.02em;
}
.timeline__title { font-family: var(--font-sans); font-size: 1rem; font-weight: 600; color: var(--text); }
.timeline__detail { font-size: 0.9rem; color: var(--text-secondary); margin-top: 0.15rem; }

/* === Cards === */
.card {
  background: var(--card-bg);
  border: 1px solid var(--card-border);
  border-radius: 8px;
  padding: 1.25rem 1.5rem;
  margin-bottom: 1rem;
  transition: background-color 0.3s ease, border-color 0.3s ease, box-shadow 0.2s;
}
.card:hover { box-shadow: 0 2px 16px rgba(0,0,0,0.05); }
.card__title { font-family: var(--font-sans); font-size: 1rem; font-weight: 600; margin-bottom: 0.4rem; color: var(--text); }
.card__meta {
  display: flex; flex-wrap: wrap; gap: 0.5rem 1.5rem;
  font-size: 0.85rem; color: var(--text-muted);
  margin-bottom: 0.4rem;
}
.card__context { font-size: 0.9rem; color: var(--text-secondary); }
.card__context a { font-weight: 500; }

/* Project report card — compact */
.card--project { padding: 1rem 1.25rem; }
.card--project .card__title { font-size: 0.95rem; }
.card--project .card__meta { margin-bottom: 0; }

/* Conference — compact list */
.conference-list { list-style: none; }
.conference-list li {
  padding: 0.65rem 0;
  border-bottom: 1px solid var(--card-border);
  font-size: 0.95rem;
  transition: border-color 0.3s ease;
}
.conference-list li:last-child { border-bottom: none; }
.conference-list .conf-date { font-size: 0.8rem; color: var(--text-muted); display: block; }

/* === Course list (Teaching) === */
.teaching-semester { margin-bottom: 1.5rem; }
.teaching-semester__title {
  font-size: 0.8rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-muted);
  margin-bottom: 0.5rem;
}
.course-item {
  display: flex; gap: 0.4rem;
  padding: 0.25rem 0;
  font-size: 0.95rem;
}
.course-item__code {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  color: var(--text-muted);
  white-space: nowrap;
}

/* === Code project cards === */
.code-project { margin-bottom: 1.5rem; }
.code-project__title {
  font-family: var(--font-serif);
  font-size: 1.2rem;
  font-weight: 600;
  margin-bottom: 0.5rem;
}
.code-project__title a { color: var(--text); }
.code-project__title a:hover { color: var(--accent); text-decoration: none; }

/* === Map icon === */
.map-icon-link {
  display: inline-flex; align-items: center; vertical-align: middle;
  color: var(--accent);
  margin-left: 0.25rem;
  transition: color 0.2s, transform 0.2s;
}
.map-icon-link:hover { color: var(--link-hover); transform: scale(1.15); text-decoration: none; }

/* === Footer === */
.footer {
  text-align: center;
  padding: 3rem 0 2rem;
  font-size: 0.8rem;
  color: var(--text-muted);
  border-top: 1px solid var(--card-border);
  transition: border-color 0.3s ease;
}

/* === Responsive === */
@media (max-width: 640px) {
  .nav__links { gap: 0.75rem; }
  .nav__links a { font-size: 0.78rem; }
  .timeline__item { grid-template-columns: 1fr; gap: 0.15rem; }
  .timeline__date { text-align: left; }
  .theorem-figure__image { max-width: 100%; }
  .section { padding: 3rem 0; }
}

@media (max-width: 480px) {
  .nav__inner { flex-wrap: wrap; gap: 0.5rem; }
  .nav__links { width: 100%; justify-content: flex-start; }
}

/* === Print === */
@media print {
  .nav, .footer, #theme-toggle { display: none; }
  body { background: #fff; color: #000; }
  .theorem { border-left-color: #000; background: none; }
}