/* Chenxi Xiao — personal site. Design harmonized with the RIM Lab site:
   Inter font, indigo-600 accent, white / gray-50 surfaces, rounded-2xl cards. */

@import url('https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600;700;800&display=swap');

:root {
  --font-sans: "Inter", ui-sans-serif, system-ui, -apple-system, sans-serif;
  --indigo: #4f46e5;
  --indigo-dark: #4338ca;
  --indigo-50: #eef2ff;
  --indigo-100: #e0e7ff;
  --gray-50: #f9fafb;
  --gray-100: #f3f4f6;
  --gray-200: #e5e7eb;
  --gray-500: #6b7280;
  --gray-600: #4b5563;
  --gray-700: #374151;
  --gray-900: #111827;
  --maxw: 1180px;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  font-family: var(--font-sans);
  color: var(--gray-900);
  background: #fff;
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}

::selection { background: var(--indigo-100); color: var(--indigo-dark); }

a { color: var(--indigo); text-decoration: none; transition: color .15s; }
a:hover { color: var(--indigo-dark); }

/* ---------- Top nav ---------- */
.nav {
  position: sticky; top: 0; z-index: 50;
  background: rgba(255,255,255,.8);
  backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--gray-100);
}
.nav__inner {
  max-width: var(--maxw); margin: 0 auto;
  display: flex; align-items: center; justify-content: space-between;
  height: 60px; padding: 0 20px;
}
.nav__brand { font-weight: 800; font-size: 1.05rem; color: var(--gray-900); letter-spacing: -.01em; }
.nav__brand span { color: var(--indigo); }
.nav__links { display: flex; gap: 26px; }
.nav__links a { color: var(--gray-600); font-weight: 500; font-size: .95rem; }
.nav__links a:hover { color: var(--gray-900); }
.nav__toggle { display: none; background: none; border: 0; cursor: pointer; color: var(--gray-600); }

/* ---------- Layout ---------- */
.shell {
  max-width: var(--maxw); margin: 0 auto; padding: 36px 20px 60px;
  display: grid; grid-template-columns: 280px 1fr; gap: 48px; align-items: start;
}

/* ---------- Sidebar ---------- */
.sidebar { position: sticky; top: 84px; }
.sidebar__photo {
  width: 100%; max-width: 220px; aspect-ratio: 1/1; object-fit: cover;
  border-radius: 18px; border: 1px solid var(--gray-200);
}
.sidebar__name { font-size: 1.5rem; font-weight: 800; margin: 18px 0 2px; letter-spacing: -.02em; }
.sidebar__title { color: var(--indigo); font-weight: 600; font-size: 1rem; margin: 0 0 2px; }
.sidebar__affil { color: var(--gray-600); font-size: .92rem; margin: 0 0 4px; }
.sidebar__loc { color: var(--gray-500); font-size: .88rem; margin: 0 0 18px; }

.pills { display: flex; flex-wrap: wrap; gap: 6px; margin-bottom: 20px; }
.pills span {
  font-size: .74rem; font-weight: 500; color: var(--gray-700);
  background: var(--gray-100); border: 1px solid var(--gray-200);
  padding: 4px 10px; border-radius: 999px;
}

.side-links { list-style: none; padding: 0; margin: 0; display: flex; flex-direction: column; gap: 9px; }
.side-links li { display: flex; align-items: center; gap: 9px; font-size: .9rem; }
.side-links a { color: var(--gray-700); display: inline-flex; align-items: center; gap: 9px; }
.side-links a:hover { color: var(--indigo); }
.side-links .ico { width: 17px; height: 17px; flex: none; color: var(--gray-500); }
.side-links a:hover .ico { color: var(--indigo); }

/* ---------- Main content ---------- */
main { min-width: 0; }
section { padding: 8px 0 40px; }
section + section { border-top: 1px solid var(--gray-100); }
h2 {
  font-size: 1.6rem; font-weight: 800; letter-spacing: -.02em; margin: 0 0 6px;
}
.section__sub { color: var(--gray-600); margin: 0 0 22px; font-size: 1rem; }
.lead { font-size: 1.05rem; color: var(--gray-700); margin: 14px 0 0; }

/* ---------- Research cards ---------- */
.research-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 20px; }
.card {
  background: #fff; border: 1px solid var(--gray-100); border-radius: 16px;
  overflow: hidden; transition: box-shadow .2s, transform .2s;
}
.card:hover { box-shadow: 0 8px 24px rgba(17,24,39,.08); transform: translateY(-2px); }
.card img { width: 100%; height: 150px; object-fit: cover; display: block; background: var(--gray-50); }
.card__body { padding: 18px; }
.card__body h3 { font-size: 1.08rem; font-weight: 700; margin: 0 0 8px; }
.card__body p { font-size: .9rem; color: var(--gray-600); margin: 0; line-height: 1.55; }

/* ---------- Publications ---------- */
.pub {
  display: grid; grid-template-columns: 230px 1fr; gap: 22px;
  background: #fff; border: 1px solid var(--gray-100); border-radius: 16px;
  padding: 18px; margin-bottom: 18px; transition: box-shadow .2s;
}
.pub:hover { box-shadow: 0 6px 18px rgba(17,24,39,.07); }
.pub__img {
  width: 100%; height: 140px; object-fit: cover; border-radius: 12px;
  background: var(--gray-50); display: block;
}
.pub__title { font-size: 1.08rem; font-weight: 700; margin: 0 0 8px; line-height: 1.35; color: var(--gray-900); }
.pub__authors { font-size: .92rem; color: var(--gray-600); margin: 0 0 6px; }
.pub__authors strong { color: var(--gray-900); font-weight: 700; }
.pub__venue { font-size: .85rem; font-weight: 600; color: var(--indigo); margin: 0 0 12px; }
.pub__links { display: flex; flex-wrap: wrap; gap: 10px; }
.btn {
  display: inline-flex; align-items: center; gap: 6px;
  font-size: .82rem; font-weight: 600; color: var(--gray-700);
  background: var(--gray-100); padding: 7px 14px; border-radius: 9px;
  transition: background .15s, color .15s;
}
.btn:hover { background: var(--gray-200); color: var(--gray-900); }
.btn svg { width: 14px; height: 14px; }

.toggle-more {
  display: flex; align-items: center; gap: 8px; margin: 24px auto 0;
  padding: 9px 22px; background: #fff; border: 1px solid var(--gray-200);
  border-radius: 999px; color: var(--gray-700); font-weight: 600; font-size: .9rem;
  cursor: pointer; transition: background .15s, color .15s;
}
.toggle-more:hover { background: var(--gray-50); color: var(--indigo); }
.toggle-more svg { width: 16px; height: 16px; transition: transform .2s; }
.toggle-more.is-open svg { transform: rotate(180deg); }
.pub.collapsed { display: none; }

/* ---------- Highlights timeline ---------- */
.timeline { position: relative; border-left: 2px solid var(--gray-200); margin-left: 6px; padding-left: 26px; }
.tl-item { position: relative; margin-bottom: 22px; }
.tl-item::before {
  content: ""; position: absolute; left: -33px; top: 4px;
  width: 13px; height: 13px; border-radius: 50%;
  background: var(--indigo); border: 3px solid #fff; box-shadow: 0 0 0 2px var(--indigo-100);
}
.tl-date { display: inline-block; font-size: .78rem; font-weight: 700; color: var(--indigo);
  background: var(--indigo-50); padding: 3px 10px; border-radius: 999px; margin-bottom: 6px; }
.tl-text { color: var(--gray-700); font-size: .95rem; margin: 0; }

/* ---------- Footer ---------- */
footer { border-top: 1px solid var(--gray-100); padding: 28px 20px; text-align: center; color: var(--gray-500); font-size: .85rem; }
footer a { color: var(--gray-600); }

/* ---------- Responsive ---------- */
@media (max-width: 900px) {
  .shell { grid-template-columns: 1fr; gap: 28px; padding-top: 24px; }
  .sidebar { position: static; display: flex; flex-direction: column; align-items: center; text-align: center; }
  .sidebar__photo { max-width: 180px; }
  .pills, .side-links { align-items: center; }
  .side-links { align-items: stretch; }
  .research-grid { grid-template-columns: 1fr; }
  .pub { grid-template-columns: 1fr; }
  .pub__img { height: 180px; }
  .nav__links { display: none; position: absolute; top: 60px; left: 0; right: 0; flex-direction: column;
    background: #fff; border-bottom: 1px solid var(--gray-100); padding: 10px 20px; gap: 4px; }
  .nav__links.is-open { display: flex; }
  .nav__links a { padding: 10px 0; }
  .nav__toggle { display: inline-flex; }
}