/* =========================================================================
   Hollen (Haoran) Zhang — academic site
   Minimal & modern. Theming via CSS custom properties (light / dark).
   ========================================================================= */

:root {
  --bg: #ffffff;
  --surface: #f7f8fa;
  --surface-2: #eef1f5;
  --text: #14171c;
  --muted: #5b6573;
  --border: #e6e9ee;
  --accent: #2f5bd7;
  --accent-soft: #eaf0ff;
  --shadow: 0 1px 2px rgba(16, 24, 40, .04), 0 6px 20px rgba(16, 24, 40, .06);
  --radius: 14px;
  --radius-sm: 9px;
  --maxw: 1080px;
  --maxw-wide: 1140px;
  --font-sans: "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  --font-serif: "Newsreader", Georgia, "Times New Roman", serif;
}

[data-theme="dark"] {
  --bg: #0f1115;
  --surface: #161a21;
  --surface-2: #1d222b;
  --text: #e8ebf0;
  --muted: #9aa4b2;
  --border: #262c36;
  --accent: #86a8ff;
  --accent-soft: #1a2440;
  --shadow: 0 1px 2px rgba(0, 0, 0, .3), 0 8px 24px rgba(0, 0, 0, .35);
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: var(--font-sans);
  font-size: 17px;
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
  transition: background-color .25s ease, color .25s ease;
}

h1, h2, h3, h4 { line-height: 1.2; font-weight: 650; letter-spacing: -0.01em; }
h1 { font-size: 2.1rem; margin: 0 0 .3em; }
h2 { font-size: 1.45rem; margin: 0 0 .6em; }
h3 { font-size: 1.12rem; margin: 0 0 .35em; }
p { margin: 0 0 1em; }

a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; text-underline-offset: 2px; }

img { max-width: 100%; display: block; }

:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
  border-radius: 4px;
}

.page {
  max-width: var(--maxw);
  margin: 0 auto;
  padding: 3.2rem 1.25rem 4rem;
}

/* ---------- Navigation ---------- */
.site-nav {
  position: sticky;
  top: 0;
  z-index: 50;
  background: color-mix(in srgb, var(--bg) 82%, transparent);
  backdrop-filter: saturate(160%) blur(12px);
  border-bottom: 1px solid var(--border);
}
.nav-inner {
  max-width: var(--maxw-wide);
  margin: 0 auto;
  padding: .7rem 1.25rem;
  display: flex;
  align-items: center;
  gap: 1rem;
}
.nav-brand {
  font-weight: 680;
  color: var(--text);
  letter-spacing: -0.02em;
  white-space: nowrap;
}
.nav-brand:hover { text-decoration: none; color: var(--accent); }
.nav-links {
  display: flex;
  gap: .25rem;
  margin-left: auto;
  flex-wrap: wrap;
  align-items: center;
}
.nav-links a {
  color: var(--muted);
  font-size: .92rem;
  font-weight: 500;
  padding: .35rem .6rem;
  border-radius: 8px;
}
.nav-links a:hover { color: var(--text); background: var(--surface); text-decoration: none; }
.nav-links a.active { color: var(--accent); background: var(--accent-soft); }

.theme-toggle {
  display: inline-grid;
  place-items: center;
  width: 36px; height: 36px;
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text);
  border-radius: 9px;
  cursor: pointer;
  transition: background .2s ease, border-color .2s ease;
}
.theme-toggle:hover { background: var(--surface-2); }
.theme-toggle .icon-moon { display: none; }
[data-theme="dark"] .theme-toggle .icon-sun { display: none; }
[data-theme="dark"] .theme-toggle .icon-moon { display: block; }

/* ---------- Hero ---------- */
.hero {
  display: flex;
  gap: 2rem;
  align-items: center;
  margin-bottom: 2.6rem;
}
.hero-photo {
  flex: 0 0 auto;
  width: 168px; height: 168px;
  border-radius: 50%;
  object-fit: cover;
  border: 1px solid var(--border);
  box-shadow: var(--shadow);
}
.hero-body { flex: 1 1 auto; min-width: 0; }
.hero-body h1 { margin-bottom: .15em; }
.hero-role { font-size: 1.05rem; color: var(--text); margin: 0 0 .15em; font-weight: 500; }
.hero-affil { color: var(--muted); margin: 0 0 .9rem; font-size: .98rem; }
.hero-affil a { font-weight: 500; }

/* social icon row */
.social { list-style: none; display: flex; gap: .55rem; padding: 0; margin: 0; flex-wrap: wrap; }
.social a {
  display: inline-grid; place-items: center;
  width: 38px; height: 38px;
  border: 1px solid var(--border);
  border-radius: 10px;
  color: var(--muted);
  background: var(--surface);
  transition: color .2s, border-color .2s, transform .15s, background .2s;
}
.social a:hover { color: var(--accent); border-color: var(--accent); transform: translateY(-2px); text-decoration: none; }

/* ---------- Sections ---------- */
.section { margin: 2.8rem 0; }
.section-head {
  display: flex; align-items: baseline; justify-content: space-between;
  gap: 1rem; margin-bottom: 1.1rem;
  border-bottom: 1px solid var(--border); padding-bottom: .5rem;
}
.section-head h2 { margin: 0; }
.section-head .more { font-size: .9rem; font-weight: 500; white-space: nowrap; }
.eyebrow {
  text-transform: uppercase; letter-spacing: .12em; font-size: .72rem;
  font-weight: 600; color: var(--accent); margin-bottom: .4rem;
}
.lead { font-size: 1.08rem; }
.muted { color: var(--muted); }

/* Keep long-form text at a comfortable reading measure inside the wider layout */
#about p, .lead { max-width: 72ch; }
.card-desc, .pub-title, .pub-authors, .pub-venue { max-width: 76ch; }

/* ---------- Link badges / pills ---------- */
.badges { display: flex; flex-wrap: wrap; gap: .4rem; margin-top: .6rem; }
.badge {
  display: inline-flex; align-items: center; gap: .3rem;
  font-size: .8rem; font-weight: 500;
  padding: .2rem .6rem;
  border: 1px solid var(--border);
  border-radius: 999px;
  color: var(--muted);
  background: var(--surface);
}
.badge:hover { color: var(--accent); border-color: var(--accent); text-decoration: none; }
.badge.is-todo { border-style: dashed; opacity: .8; }

/* ---------- Publications ---------- */
.pub-group + .pub-group { margin-top: 1.6rem; }
.pub-year {
  font-family: var(--font-serif); font-size: 1.5rem; color: var(--muted);
  font-weight: 500; margin: 0 0 .6rem;
}
.pub {
  padding: 1rem 0;
  border-top: 1px solid var(--border);
}
.pub:first-of-type { border-top: none; }
.pub-title { font-weight: 600; margin: 0 0 .2rem; font-size: 1.04rem; }
.pub-title a { color: var(--text); }
.pub-title a:hover { color: var(--accent); }
.pub-authors { color: var(--muted); font-size: .95rem; margin: 0 0 .15rem; }
.pub-authors .me { color: var(--text); font-weight: 600; }
.pub-venue { font-style: italic; color: var(--muted); font-size: .95rem; margin: 0; }
.tag {
  display: inline-block; font-size: .68rem; font-weight: 700; letter-spacing: .06em;
  text-transform: uppercase; padding: .12rem .45rem; border-radius: 6px;
  background: var(--accent-soft); color: var(--accent); vertical-align: middle;
  margin-left: .4rem;
}
.tag.draft { background: var(--surface-2); color: var(--muted); }

/* ---------- Project cards ---------- */
.cards { display: flex; flex-direction: column; gap: 1.1rem; }
.card {
  display: flex; gap: 1.1rem;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--surface);
  overflow: hidden;
  transition: transform .18s ease, box-shadow .18s ease, border-color .18s ease;
}
.card:hover { transform: translateY(-2px); box-shadow: var(--shadow); border-color: color-mix(in srgb, var(--accent) 40%, var(--border)); }
.card-thumb {
  flex: 0 0 180px;
  background: var(--surface-2);
}
.card-thumb img { width: 100%; height: 100%; object-fit: cover; min-height: 150px; }
.card-thumb.placeholder { display: grid; place-items: center; color: var(--muted); font-family: var(--font-serif); font-size: 2rem; }
.card-body { padding: 1.1rem 1.2rem 1.15rem 0; flex: 1 1 auto; min-width: 0; }
.card-body.no-thumb { padding-left: 1.2rem; }
.card-title { margin: 0 0 .25rem; font-size: 1.08rem; }
.card-title a { color: var(--text); }
.card-title a:hover { color: var(--accent); }
.card-meta { font-size: .88rem; color: var(--muted); margin: 0 0 .55rem; }
.card-meta .role { color: var(--accent); font-weight: 600; }
.card-desc { margin: 0; font-size: .96rem; }

/* ---------- Lists (service, awards, presentations, news) ---------- */
.timeline { list-style: none; padding: 0; margin: 0; }
.timeline li {
  display: grid;
  grid-template-columns: 8.5rem 1fr;
  gap: 1rem;
  padding: .7rem 0;
  border-top: 1px solid var(--border);
}
.timeline li:first-child { border-top: none; }
.timeline .when { color: var(--muted); font-size: .9rem; font-variant-numeric: tabular-nums; }
.timeline .what { margin: 0; }
.timeline .what strong { font-weight: 600; }
.timeline .sub { color: var(--muted); font-size: .92rem; }

.news { list-style: none; padding: 0; margin: 0; }
.news li { display: grid; grid-template-columns: 6.5rem 1fr; gap: 1rem; padding: .5rem 0; }
.news .when { color: var(--muted); font-size: .88rem; }

.chips { display: flex; flex-wrap: wrap; gap: .45rem; margin: .4rem 0 0; padding: 0; list-style: none; }
.chips li {
  font-size: .85rem; padding: .25rem .65rem; border-radius: 8px;
  background: var(--surface); border: 1px solid var(--border); color: var(--text);
}

.callout {
  border: 1px dashed var(--border);
  background: var(--surface);
  border-radius: var(--radius-sm);
  padding: .8rem 1rem;
  font-size: .92rem;
  color: var(--muted);
  margin: 1rem 0;
}

.btn {
  display: inline-flex; align-items: center; gap: .45rem;
  background: var(--accent); color: #fff;
  padding: .55rem 1rem; border-radius: 10px; font-weight: 550; font-size: .95rem;
  border: 1px solid transparent;
}
[data-theme="dark"] .btn { color: #0f1115; }
.btn:hover { text-decoration: none; opacity: .92; }
.btn.ghost { background: transparent; color: var(--text); border-color: var(--border); }
.btn.ghost:hover { border-color: var(--accent); color: var(--accent); opacity: 1; }

/* ---------- Footer ---------- */
.site-footer { border-top: 1px solid var(--border); margin-top: 2rem; }
.footer-inner {
  max-width: var(--maxw); margin: 0 auto; padding: 2rem 1.25rem 2.6rem;
  display: flex; flex-direction: column; gap: .8rem; align-items: center; text-align: center;
}
.footer-meta { color: var(--muted); font-size: .88rem; margin: 0; }
.footer-meta .dot { margin: 0 .2rem; }

/* ---------- Responsive ---------- */
@media (max-width: 640px) {
  body { font-size: 16px; }
  h1 { font-size: 1.8rem; }
  .hero { flex-direction: column; text-align: center; gap: 1.2rem; }
  .hero-photo { width: 132px; height: 132px; }
  .social { justify-content: center; }
  .card { flex-direction: column; }
  .card-thumb { flex-basis: auto; }
  .card-thumb img { min-height: 0; aspect-ratio: 16 / 9; }
  .card-body { padding: 0 1.1rem 1.1rem; }
  .timeline li, .news li { grid-template-columns: 1fr; gap: .15rem; }
  .nav-brand { font-size: .95rem; }
  .nav-links a { padding: .35rem .45rem; }
}

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