/* =============================================================================
   Zetao Yang — Personal Homepage Stylesheet
   Modern academic style, inspired by randomtutu.github.io's design system.
   ============================================================================= */

:root {
  --primary:        #134e4a;   /* deep teal */
  --accent:         #0d9488;   /* teal-600 */
  --accent-light:   #ccfbf1;   /* teal-100 */
  --text:           #1f2937;
  --text-secondary: #6b7280;
  --bg:             #f7fdfb;   /* hint of teal in bg */
  --card-bg:        #ffffff;
  --border:         #e5e7eb;
  --shadow:         0 1px 3px rgba(0,0,0,.06), 0 1px 2px rgba(0,0,0,.04);
  --shadow-md:      0 4px 6px rgba(0,0,0,.05), 0 2px 4px rgba(0,0,0,.04);
  --shadow-lg:      0 10px 15px rgba(0,0,0,.06), 0 4px 6px rgba(0,0,0,.04);
  --radius:         12px;
  --max-width:      880px;
}

* { margin: 0; padding: 0; box-sizing: border-box; }

html { scroll-behavior: smooth; scroll-padding-top: 80px; }

body {
  font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  color: var(--text);
  background: var(--bg);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}

a {
  color: var(--accent);
  text-decoration: none;
  transition: color .2s;
}
a:hover { color: var(--primary); }

/* ── Navbar ──────────────────────────────────────────── */
.navbar {
  position: fixed;
  top: 0; left: 0; right: 0;
  z-index: 100;
  background: rgba(255,255,255,.85);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid rgba(0,0,0,.06);
  transition: box-shadow .3s;
}
.navbar.scrolled { box-shadow: var(--shadow-md); }

.navbar-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 24px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 60px;
}

.brand {
  font-weight: 700;
  font-size: 1.05rem;
  color: var(--primary);
  letter-spacing: -.02em;
}

.nav-links {
  display: flex;
  gap: 8px;
  list-style: none;
}
.nav-links a {
  color: var(--text-secondary);
  font-size: .88rem;
  font-weight: 500;
  padding: 6px 12px;
  border-radius: 6px;
  transition: all .2s;
}
.nav-links a:hover {
  color: var(--accent);
  background: var(--accent-light);
}

.hamburger {
  display: none;
  background: none;
  border: none;
  cursor: pointer;
  padding: 6px;
  flex-direction: column;
  gap: 5px;
}
.hamburger span {
  display: block;
  width: 22px;
  height: 2px;
  background: var(--text);
  border-radius: 1px;
  transition: transform .3s, opacity .3s;
}
.hamburger.active span:nth-child(1) { transform: translateY(7px) rotate(45deg); }
.hamburger.active span:nth-child(2) { opacity: 0; }
.hamburger.active span:nth-child(3) { transform: translateY(-7px) rotate(-45deg); }

/* ── Container ──────────────────────────────────────── */
.container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 80px 24px 60px;
}

/* ── Hero ──────────────────────────────────────────── */
.hero {
  display: flex;
  align-items: center;
  gap: 40px;
  padding: 48px 0 32px;
}

.hero-text { flex: 1; }

.hero-text h1 {
  font-size: 2rem;
  font-weight: 800;
  color: var(--primary);
  letter-spacing: -.03em;
  margin-bottom: 4px;
}
.hero-text h1 .cn {
  font-weight: 400;
  font-size: .6em;
  color: var(--text-secondary);
  margin-left: 8px;
}

.hero-text .subtitle {
  font-size: 1rem;
  color: var(--text-secondary);
  margin-bottom: 8px;
}

.hero-text .quote {
  font-family: 'Inter', sans-serif;
  font-size: 1rem;
  color: var(--text-secondary);
  margin-top: 14px;
  padding: 6px 0 6px 14px;
  border-left: 3px solid var(--accent);
  line-height: 1.6;
  overflow-x: auto;
}
.hero-text .quote .katex { font-size: .9em; }

.hero-text .quote-caption {
  font-size: .85rem;
  color: var(--text-secondary);
  font-style: italic;
  margin-top: 6px;
  line-height: 1.5;
}

.profile-img {
  width: 160px;
  height: 160px;
  border-radius: 50%;
  object-fit: cover;
  border: 4px solid var(--card-bg);
  box-shadow: var(--shadow-lg);
  flex-shrink: 0;
}
.profile-placeholder {
  width: 160px;
  height: 160px;
  border-radius: 50%;
  background: linear-gradient(135deg, var(--accent), var(--primary));
  display: flex;
  align-items: center;
  justify-content: center;
  color: #fff;
  font-size: 3rem;
  font-weight: 700;
  flex-shrink: 0;
  box-shadow: var(--shadow-lg);
}

/* ── Section Cards ──────────────────────────────────── */
.section {
  background: var(--card-bg);
  border-radius: var(--radius);
  padding: 32px;
  margin-bottom: 24px;
  box-shadow: var(--shadow);
  border: 1px solid var(--border);
}

.section h2 {
  font-size: 1.3rem;
  font-weight: 700;
  color: var(--primary);
  margin-bottom: 20px;
  padding-bottom: 10px;
  border-bottom: 2px solid var(--accent-light);
  display: flex;
  align-items: center;
  gap: 10px;
}
.section h2 i {
  color: var(--accent);
  font-size: 1.1rem;
}

.bio-text {
  font-size: .95rem;
  line-height: 1.8;
  color: var(--text);
  margin-bottom: 16px;
}
.bio-text:last-child { margin-bottom: 0; }

/* ── Biography Grid (Interests + Contact) ──────────── */
.bio-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 16px;
  margin-top: 16px;
}
.bio-card {
  background: var(--bg);
  border-radius: 10px;
  padding: 18px;
  border: 1px solid var(--border);
  transition: transform .2s, box-shadow .2s;
}
.bio-card:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}
.bio-card h4 {
  font-size: .85rem;
  font-weight: 600;
  color: var(--text-secondary);
  margin-bottom: 12px;
  text-transform: uppercase;
  letter-spacing: .05em;
}

.interest-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}
.interest-tag {
  font-size: .8rem;
  font-weight: 500;
  padding: 4px 12px;
  border-radius: 20px;
  background: var(--accent-light);
  color: var(--accent);
}

.contact-links {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}
.contact-btn {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 8px 14px;
  font-size: .85rem;
  font-weight: 500;
  color: var(--text-secondary);
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  cursor: pointer;
  transition: all .2s;
}
.contact-btn:hover {
  color: var(--accent);
  border-color: var(--accent);
  transform: translateY(-1px);
  box-shadow: var(--shadow);
}
.contact-btn i { font-size: .95rem; }

/* ── News Timeline ──────────────────────────────────── */
.news-list {
  position: relative;
  padding-left: 24px;
  list-style: none;
}
.news-list::before {
  content: '';
  position: absolute;
  left: 5px; top: 8px; bottom: 8px;
  width: 2px;
  background: linear-gradient(to bottom, var(--accent-light), transparent);
  border-radius: 1px;
}
.news-item {
  position: relative;
  padding: 0 0 20px 20px;
  font-size: .9rem;
  line-height: 1.6;
}
.news-item::before {
  content: '';
  position: absolute;
  left: -22px; top: 8px;
  width: 8px; height: 8px;
  border-radius: 50%;
  background: var(--accent);
  border: 2px solid var(--card-bg);
  box-shadow: 0 0 0 2px var(--accent-light);
  transition: transform .2s;
}
.news-item:hover::before { transform: scale(1.3); }

.news-date {
  font-weight: 600;
  color: var(--text-secondary);
  font-size: .82rem;
  font-variant-numeric: tabular-nums;
}
.news-text { color: var(--text); margin-top: 2px; }
.news-text em { font-style: italic; }
.news-text .venue { font-weight: 600; color: var(--primary); }

/* ── Research thesis + list ─────────────────────────── */
.research-thesis {
  font-size: 1rem;
  color: var(--text);
  margin-bottom: 16px;
  padding: 12px 16px;
  background: var(--accent-light);
  border-radius: 8px;
}

.research-list {
  list-style: none;
  counter-reset: research-counter;
  margin-top: 8px;
}
.research-item {
  counter-increment: research-counter;
  position: relative;
  padding: 14px 0 14px 36px;
  border-bottom: 1px solid var(--border);
}
.research-item:last-child {
  border-bottom: none;
  padding-bottom: 0;
}
.research-item::before {
  content: counter(research-counter) ".";
  position: absolute;
  left: 0; top: 14px;
  font-weight: 700;
  font-size: 1rem;
  color: var(--accent);
}
.research-title {
  font-size: .95rem;
  font-weight: 700;
  color: var(--primary);
  margin-bottom: 6px;
}
.research-desc {
  font-size: .88rem;
  color: var(--text-secondary);
  line-height: 1.7;
}
.research-desc .venue { font-weight: 600; color: var(--primary); }

/* ── Publication card ───────────────────────────────── */
.pub-card {
  padding: 20px 0;
  border-bottom: 1px solid var(--border);
}
.pub-card:last-child {
  border-bottom: none;
  padding-bottom: 0;
}
.pub-card:first-of-type { padding-top: 0; }

.pub-title {
  font-weight: 700;
  color: var(--primary);
  font-size: 1rem;
  margin-bottom: 6px;
  line-height: 1.4;
}
.pub-authors {
  font-size: .88rem;
  color: var(--text);
  margin-bottom: 4px;
}
.pub-authors .me { font-weight: 700; }

.pub-venue {
  font-size: .85rem;
  color: var(--text-secondary);
  margin-bottom: 8px;
}
.pub-venue .venue-name { font-weight: 600; color: var(--primary); }

.pub-links {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  margin-top: 4px;
  margin-bottom: 10px;
}
.pub-link {
  font-size: .8rem;
  padding: 3px 10px;
  background: var(--accent-light);
  color: var(--accent);
  border-radius: 4px;
  font-weight: 500;
}

.pub-abstract {
  font-size: .88rem;
  color: var(--text-secondary);
  line-height: 1.6;
}

/* ── Experience / Education cards ─────────────────── */
.timeline-card {
  padding: 16px 0;
  border-bottom: 1px solid var(--border);
}
.timeline-card:last-child { border-bottom: none; padding-bottom: 0; }
.timeline-card:first-of-type { padding-top: 0; }

.timeline-head {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  flex-wrap: wrap;
  gap: 8px;
  margin-bottom: 4px;
}
.timeline-title {
  font-weight: 700;
  color: var(--primary);
  font-size: 1rem;
}
.timeline-date {
  color: var(--text-secondary);
  font-size: .85rem;
  font-variant-numeric: tabular-nums;
}
.timeline-role {
  font-size: .88rem;
  color: var(--text-secondary);
  font-style: italic;
  margin-bottom: 8px;
}
.timeline-body {
  font-size: .88rem;
  color: var(--text);
  line-height: 1.6;
}
.timeline-body ul {
  padding-left: 18px;
  margin-top: 4px;
}
.timeline-body li { margin-bottom: 3px; }

/* ── Awards as compact list ─────────────────────────── */
.awards-list {
  list-style: none;
}
.awards-list li {
  padding: 10px 0;
  border-bottom: 1px solid var(--border);
  font-size: .9rem;
  line-height: 1.5;
}
.awards-list li:last-child { border-bottom: none; }
.awards-list .award-title {
  font-weight: 700;
  color: var(--primary);
}
.awards-list .award-year {
  float: right;
  color: var(--text-secondary);
  font-variant-numeric: tabular-nums;
}
.awards-list .award-topic {
  display: block;
  font-size: .82rem;
  color: var(--text-secondary);
  font-style: italic;
  margin-top: 2px;
}

/* ── Footer ─────────────────────────────────────────── */
footer {
  margin-top: 40px;
  padding: 24px 0;
  text-align: center;
  color: var(--text-secondary);
  font-size: .82rem;
}

/* ── Responsive ─────────────────────────────────────── */
@media (max-width: 768px) {
  .hamburger { display: flex; }
  .nav-links {
    display: none;
    position: absolute;
    top: 60px;
    left: 0; right: 0;
    background: rgba(255,255,255,.95);
    backdrop-filter: blur(12px);
    flex-direction: column;
    padding: 12px 24px;
    border-bottom: 1px solid var(--border);
  }
  .nav-links.active { display: flex; }
  .hero {
    flex-direction: column-reverse;
    text-align: center;
    gap: 20px;
  }
  .hero-text .quote { text-align: left; }
  .bio-grid { grid-template-columns: 1fr; }
  .section { padding: 24px; }
  .timeline-head { flex-direction: column; gap: 2px; }
}

/* ── Animation ──────────────────────────────────────── */
@keyframes fadeInUp {
  from { opacity: 0; transform: translateY(10px); }
  to   { opacity: 1; transform: translateY(0); }
}
.section { animation: fadeInUp .5s ease both; }