/* ===========================================================
   Lingsen Meng — academic homepage
   Clean academic style. System fonts only (no Google Fonts,
   so it loads fast and is not blocked behind the GFW in China).
   =========================================================== */

:root {
  --bg: #ffffff;
  --bg-soft: #f7f8fa;
  --text: #1b1d22;
  --muted: #5b6470;
  --line: #e6e8ec;
  --accent: #2774ae;        /* UCLA blue */
  --accent-dark: #154e78;
  --accent-soft: #eaf2f9;
  --maxw: 1080px;
  --radius: 12px;
  --sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto,
          "Helvetica Neue", "PingFang SC", "Hiragino Sans GB",
          "Microsoft YaHei", Arial, sans-serif;
  --serif: Georgia, "Times New Roman", "Songti SC", serif;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  font-family: var(--sans);
  color: var(--text);
  background: var(--bg);
  line-height: 1.65;
  font-size: 17px;
  -webkit-font-smoothing: antialiased;
}

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

.wrap { max-width: var(--maxw); margin: 0 auto; padding: 0 24px; }

/* ---------- Top navigation ---------- */
.nav {
  position: sticky; top: 0; z-index: 50;
  background: rgba(255,255,255,0.88);
  backdrop-filter: saturate(180%) blur(10px);
  border-bottom: 1px solid var(--line);
}
.nav-inner {
  max-width: var(--maxw); margin: 0 auto;
  display: flex; align-items: center; justify-content: space-between;
  padding: 12px 24px;
}
.nav-brand { font-weight: 700; font-size: 17px; color: var(--text); }
.nav-brand:hover { text-decoration: none; color: var(--accent-dark); }
.nav-links { display: flex; gap: 22px; flex-wrap: wrap; }
.nav-links a {
  color: var(--muted); font-weight: 500; font-size: 15.5px;
  padding: 4px 0; border-bottom: 2px solid transparent;
}
.nav-links a:hover { color: var(--accent); text-decoration: none; }
.nav-links a.active { color: var(--text); border-bottom-color: var(--accent); }

/* ---------- Hero ---------- */
.hero { padding: 56px 0 40px; }
.hero-grid {
  display: grid; grid-template-columns: 240px 1fr; gap: 44px; align-items: start;
}
.photo {
  width: 240px; height: 300px; object-fit: cover;
  border-radius: var(--radius); background: var(--bg-soft);
  border: 1px solid var(--line);
}
.photo-ph {
  width: 240px; height: 300px; border-radius: var(--radius);
  background: linear-gradient(135deg, var(--accent-soft), #dce9f4);
  border: 1px dashed #b9d2e6; display: flex; align-items: center;
  justify-content: center; color: var(--accent-dark); font-size: 14px;
  text-align: center; padding: 16px;
}
.hero h1 { font-size: 34px; margin: 0 0 6px; letter-spacing: -0.4px; }
.hero .title { font-size: 18px; color: var(--accent-dark); font-weight: 600; margin: 0; }
.hero .affil { color: var(--muted); margin: 2px 0 18px; }
.hero p.bio { font-size: 17px; margin: 0 0 18px; }

.links { display: flex; flex-wrap: wrap; gap: 10px; margin-top: 8px; }
.btn {
  display: inline-flex; align-items: center; gap: 7px;
  padding: 7px 14px; border-radius: 999px; font-size: 14.5px; font-weight: 500;
  border: 1px solid var(--line); background: #fff; color: var(--text);
}
.btn:hover { border-color: var(--accent); color: var(--accent); text-decoration: none; }
.btn-primary { background: var(--accent); color: #fff; border-color: var(--accent); }
.btn-primary:hover { background: var(--accent-dark); color: #fff; border-color: var(--accent-dark); }

/* ---------- Metrics ---------- */
.metrics {
  display: flex; gap: 14px; flex-wrap: wrap; margin: 8px 0 0;
}
.metric {
  background: var(--bg-soft); border: 1px solid var(--line);
  border-radius: var(--radius); padding: 12px 18px; text-align: center; min-width: 110px;
}
.metric .num { font-size: 24px; font-weight: 700; color: var(--accent-dark); }
.metric .lab { font-size: 12.5px; color: var(--muted); text-transform: uppercase; letter-spacing: .5px; }

/* ---------- Sections ---------- */
section { padding: 40px 0; border-top: 1px solid var(--line); }
section h2 {
  font-family: var(--serif); font-size: 26px; margin: 0 0 22px;
  letter-spacing: -0.2px;
}
.lead { color: var(--muted); max-width: 760px; }

/* Table of contents */
.toc {
  background: var(--bg-soft); border: 1px solid var(--line);
  border-radius: var(--radius); padding: 18px 24px; margin: 8px 0 0;
}
.toc h4 { margin: 0 0 10px; font-size: 13px; text-transform: uppercase; letter-spacing: .6px; color: var(--muted); }
.toc ul { margin: 0; padding-left: 18px; columns: 2; column-gap: 32px; }
.toc li { margin: 5px 0; break-inside: avoid; }

/* Research subsections */
.subsec { margin-top: 26px; }
.subsec h3 { font-size: 19px; margin: 0 0 8px; color: var(--accent-dark); }
.subsec p { margin: 0; }
.ref { color: var(--muted); }
.figcap { color: var(--muted); font-size: 14px; font-style: italic; margin-top: 8px; border-left: 3px solid var(--line); padding-left: 12px; }

/* Figures */
.fig { margin: 18px 0 4px; }
.fig img {
  width: 100%; max-width: 760px; height: auto; display: block;
  border: 1px solid var(--line); border-radius: 8px; background: #fff;
}
.fig figcaption { color: var(--muted); font-size: 14px; font-style: italic; margin-top: 8px; max-width: 760px; line-height: 1.5; }

/* News */
.news-list { list-style: none; padding: 0; margin: 0; }
.news-list li {
  display: grid; grid-template-columns: 92px 1fr; gap: 16px;
  padding: 12px 0; border-bottom: 1px solid var(--line);
}
.news-list li:last-child { border-bottom: none; }
.news-date { color: var(--accent-dark); font-weight: 600; font-size: 14.5px; }

/* Research cards */
.cards { display: grid; grid-template-columns: repeat(2, 1fr); gap: 18px; }
.card {
  border: 1px solid var(--line); border-radius: var(--radius);
  padding: 22px; background: #fff; transition: box-shadow .15s, transform .15s;
}
.card:hover { box-shadow: 0 8px 28px rgba(20,40,70,.08); transform: translateY(-2px); }
a.card { color: inherit; text-decoration: none; display: block; }
a.card:hover { text-decoration: none; color: inherit; border-color: var(--accent); }
a.card h3 { color: var(--accent-dark); }
.card-thumb { width: 100%; height: 158px; object-fit: cover; border-radius: 8px; border: 1px solid var(--line); margin-bottom: 14px; background: #fff; }

/* Topic sub-page chrome */
.breadcrumb { color: var(--muted); font-size: 14px; margin: 0 0 6px; }
.breadcrumb a { color: var(--muted); }
.breadcrumb a:hover { color: var(--accent); }
.prevnext { display: flex; justify-content: space-between; gap: 16px; margin-top: 8px; flex-wrap: wrap; }
.prevnext a { font-size: 15px; }
.prevnext .nx { margin-left: auto; text-align: right; }
.card h3 { margin: 0 0 8px; font-size: 18px; }
.card p { margin: 0; color: var(--muted); font-size: 15.5px; }
.card .tag { font-size: 22px; }

/* ---------- Publications ---------- */
.pub-controls { margin-bottom: 18px; color: var(--muted); font-size: 15px; }
.pub-list { list-style: none; padding: 0; margin: 0; counter-reset: none; }
.pub {
  display: grid; grid-template-columns: 44px 1fr; gap: 14px;
  padding: 16px 0; border-bottom: 1px solid var(--line);
}
.pub-num {
  color: var(--muted); font-variant-numeric: tabular-nums; font-size: 14.5px; padding-top: 2px;
}
.pub-title { font-weight: 600; }
.pub-authors { color: var(--muted); font-size: 15px; }
.pub-authors .me { color: var(--text); font-weight: 700; }
.pub-venue { font-style: italic; color: #444; font-size: 15px; }
.pub-venue .year { font-style: normal; color: var(--muted); }
.pub-links { margin-top: 5px; font-size: 14px; }
.pub-links .pdf-na { color: #b6bcc4; cursor: help; }
.badge {
  display: inline-block; font-size: 11.5px; font-weight: 700; letter-spacing: .4px;
  padding: 2px 8px; border-radius: 999px; margin-left: 8px; vertical-align: middle;
  text-transform: uppercase;
}
.badge-science { background: #fde8e8; color: #b42318; }
.badge-nature { background: #e7f4ec; color: #1a7f47; }

/* ---------- Group ---------- */
.group-block { margin-bottom: 30px; }
.group-block h3 { font-size: 18px; margin: 0 0 12px; color: var(--accent-dark); }
.people { display: grid; grid-template-columns: repeat(auto-fill, minmax(220px,1fr)); gap: 10px 28px; }
.people li { list-style: none; }
.people .who { font-weight: 600; }
.people .role { color: var(--muted); font-size: 14.5px; }
ul.plain { padding-left: 0; }

/* detailed people list (alumni with current positions) */
.people.detailed { grid-template-columns: 1fr; gap: 0; }
.people.detailed li { padding: 12px 0; border-bottom: 1px solid var(--line); }
.people.detailed li:last-child { border-bottom: none; }
.people .role, .people .focus { display: block; }
.people .role { margin-top: 1px; }
.people .focus { color: var(--muted); font-size: 14.5px; margin-top: 3px; }
.people .where { color: var(--accent-dark); font-weight: 500; }
.people .me-links { font-size: 13.5px; margin-top: 3px; }
.people .me-links a { margin-right: 12px; }
.people .period { display: block; color: var(--muted); font-size: 13.5px; margin-top: 1px; }
.people .thesis { display: block; color: var(--muted); font-size: 13.5px; margin-top: 3px; }
.people .thesis a { font-style: italic; }

/* ---------- Contact ---------- */
.contact-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 10px 30px; max-width: 720px; }
.contact-grid .k { color: var(--muted); }
.email-img { height: 22px; width: auto; vertical-align: middle; display: inline-block; }

/* ---------- Footer ---------- */
footer {
  border-top: 1px solid var(--line); padding: 28px 0; margin-top: 20px;
  color: var(--muted); font-size: 14px; text-align: center;
}

/* ---------- Responsive ---------- */
@media (max-width: 760px) {
  body { font-size: 16px; }
  .hero-grid { grid-template-columns: 1fr; gap: 24px; justify-items: center; text-align: center; }
  .hero .links, .metrics { justify-content: center; }
  .hero h1 { font-size: 28px; }
  .cards, .contact-grid { grid-template-columns: 1fr; }
  .nav-links { gap: 14px; }
  .nav-brand { font-size: 15px; }
  .nav-links a { font-size: 14px; }
  .news-list li { grid-template-columns: 1fr; gap: 2px; }
  .pub { grid-template-columns: 1fr; }
  .pub-num { display: none; }
}