/* ═══════════════════════════════════════════════════════════
   Chong Liu — Personal Academic Homepage
   Clean, minimal, Notion-inspired
   ═══════════════════════════════════════════════════════════ */

/* ── Custom Properties ──────────────────────────────────── */
:root {
  --bg: #ffffff;
  --bg-alt: #f7f6f3;
  --surface: #ffffff;
  --border: #e8e8e4;
  --text: #37352f;
  --text-muted: #787774;
  --text-zh: #6b6b6b;
  --accent: #2d74da;
  --accent-hover: #1a5bb8;
  --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.08);
  --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.1);
  --radius: 8px;
  --header-h: 56px;
  --font-sans:
    -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Helvetica Neue', Arial, 'Noto Sans SC',
    sans-serif;
  --transition: 0.2s ease;
}

[data-theme='dark'] {
  --bg: #191919;
  --bg-alt: #222222;
  --surface: #2f2f2f;
  --border: #3d3d3d;
  --text: #e8e8e4;
  --text-muted: #9b9a97;
  --text-zh: #aaa9a5;
  --accent: #5b9cf6;
  --accent-hover: #7ab3ff;
  --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.3);
  --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.35);
}

/* ── Reset & Base ───────────────────────────────────────── */
*,
*::before,
*::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  scroll-behavior: smooth;
  scroll-padding-top: calc(var(--header-h) + 16px);
}

body {
  font-family: var(--font-sans);
  background: var(--bg);
  color: var(--text);
  line-height: 1.7;
  transition:
    background var(--transition),
    color var(--transition);
}

img {
  max-width: 100%;
  display: block;
}
a {
  color: var(--accent);
  text-decoration: none;
  transition: color var(--transition);
}
a:hover {
  color: var(--accent-hover);
  text-decoration: underline;
}
ul {
  list-style: none;
}

/* ── Layout ─────────────────────────────────────────────── */
.container {
  max-width: 960px;
  margin: 0 auto;
  padding: 0 24px;
}

/* ── Header ─────────────────────────────────────────────── */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  height: var(--header-h);
  background: var(--bg);
  border-bottom: 1px solid var(--border);
  backdrop-filter: blur(8px);
  transition:
    background var(--transition),
    border-color var(--transition);
}

.header-inner {
  max-width: 960px;
  margin: 0 auto;
  padding: 0 24px;
  height: 100%;
  display: flex;
  align-items: center;
  gap: 24px;
}

.header-actions {
  margin-left: auto;
  display: flex;
  gap: 8px;
  flex-shrink: 0;
}

.site-title {
  font-size: 1rem;
  font-weight: 700;
  color: var(--text);
  white-space: nowrap;
  flex-shrink: 0;
}
.site-title:hover {
  color: var(--accent);
  text-decoration: none;
}

.main-nav {
  display: flex;
  gap: 4px;
  flex-wrap: wrap;
  flex: 1;
}

.main-nav a {
  font-size: 0.8rem;
  color: var(--text-muted);
  padding: 4px 10px;
  border-radius: 4px;
  white-space: nowrap;
  transition:
    background var(--transition),
    color var(--transition);
}
.main-nav a:hover,
.main-nav a.active {
  background: var(--bg-alt);
  color: var(--text);
  text-decoration: none;
}
.main-nav a.active {
  font-weight: 600;
}

/* ── Theme Toggle ───────────────────────────────────────── */
.theme-toggle {
  flex-shrink: 0;
  background: none;
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 0.3rem 0.6rem;
  cursor: pointer;
  font-size: 0.85rem;
  color: var(--text-muted);
  transition:
    border-color var(--transition),
    background var(--transition);
  line-height: 1;
  min-width: 36px;
  text-align: center;
}
.theme-toggle:hover {
  border-color: var(--accent);
}

.icon-sun {
  display: none;
}
.icon-moon {
  display: inline;
}
[data-theme='dark'] .icon-sun {
  display: inline;
}
[data-theme='dark'] .icon-moon {
  display: none;
}

/* ── Language Toggle ─────────────────────────────────────── */
.lang-toggle {
  flex-shrink: 0;
  background: none;
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 0.3rem 0.6rem;
  cursor: pointer;
  font-size: 0.78rem;
  font-weight: 700;
  color: var(--text-muted);
  transition:
    border-color var(--transition),
    background var(--transition),
    color var(--transition);
  line-height: 1;
  user-select: none;
  min-width: 36px;
  text-align: center;
}
.lang-toggle:hover {
  background: var(--accent);
  color: #fff;
  border-color: var(--accent);
}

/* Language version display */
#lang-zh {
  display: none !important;
}
[data-lang-mode='zh'] #lang-en {
  display: none !important;
}
[data-lang-mode='zh'] #lang-zh {
  display: block !important;
}

/* ── Hero ───────────────────────────────────────────────── */
.hero {
  padding: 64px 0 56px;
  border-bottom: 1px solid var(--border);
}

.hero-grid {
  display: grid;
  grid-template-columns: 1fr 280px;
  gap: 48px;
  align-items: start;
}

.hero-name {
  font-size: 2.4rem;
  font-weight: 800;
  line-height: 1.2;
  margin-bottom: 8px;
  color: var(--text);
}
.name-zh {
  font-size: 1.6rem;
  font-weight: 600;
  color: var(--text-muted);
  margin-left: 8px;
}

/* Hero social links */
.hero-links {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  align-items: center;
  margin-bottom: 12px;
  font-size: 0.9rem;
}
.hero-links a {
  color: var(--accent);
  font-weight: 500;
}
.hero-links a:hover {
  text-decoration: underline;
}
.hero-link-sep {
  color: var(--text-muted);
  user-select: none;
}

.hero-role {
  font-size: 1.05rem;
  font-weight: 600;
  color: var(--accent);
  margin-bottom: 2px;
}
.hero-role-zh {
  font-size: 0.95rem;
  color: var(--text-zh);
  margin-bottom: 6px;
}
.hero-location {
  font-size: 0.85rem;
  color: var(--text-muted);
  margin-bottom: 28px;
}

.bio p {
  font-size: 0.95rem;
  color: var(--text);
  margin-bottom: 10px;
}
.bio .bio-zh {
  color: var(--text-zh);
  font-size: 0.88rem;
  margin-bottom: 18px;
  padding-left: 12px;
  border-left: 2px solid var(--border);
}

/* ── Profile Photo ─────────────────────────────────────── */
.hero-photo {
  display: flex;
  justify-content: center;
}

.photo-img {
  width: 240px;
  height: 300px;
  border-radius: var(--radius);
  overflow: hidden;
  box-shadow: var(--shadow-md);
}
.photo-img img {
  width: 100%;
  height: 100%;
  object-fit: cover;
  object-position: top center;
  display: block;
}

/* ── Sections ───────────────────────────────────────────── */
.section {
  padding: 56px 0;
  border-bottom: 1px solid var(--border);
}
.section-alt {
  background: var(--bg-alt);
  transition: background var(--transition);
}

.section-title {
  font-size: 1.3rem;
  font-weight: 700;
  margin-bottom: 32px;
  color: var(--text);
}
.title-zh {
  font-size: 1rem;
  font-weight: 500;
  color: var(--text-muted);
  margin-left: 8px;
}

/* ── Cards ──────────────────────────────────────────────── */
.card-list {
  display: flex;
  flex-direction: column;
  gap: 16px;
}

.card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 20px 24px;
  display: flex;
  gap: 20px;
  align-items: flex-start;
  box-shadow: var(--shadow-sm);
  transition:
    background var(--transition),
    border-color var(--transition),
    box-shadow var(--transition),
    transform var(--transition);
}
.card:hover {
  box-shadow: var(--shadow-md);
  transform: translateY(-1px);
}

.card-icon {
  font-size: 1.6rem;
  flex-shrink: 0;
  line-height: 1;
  margin-top: 2px;
}

.card-body h3 {
  font-size: 1rem;
  font-weight: 700;
  margin-bottom: 4px;
  color: var(--text);
}
.card-zh {
  font-size: 0.85rem;
  font-weight: 500;
  color: var(--text-muted);
  margin-left: 6px;
}
.card-meta {
  font-size: 0.82rem;
  color: var(--text-muted);
  margin-bottom: 6px;
}
.card-bullets {
  padding-left: 16px;
  list-style: disc;
}
.card-bullets li {
  font-size: 0.88rem;
  color: var(--text);
  margin-bottom: 4px;
}
.card-bullets .zh {
  color: var(--text-zh);
  font-size: 0.83rem;
}

/* ── Project Grid ───────────────────────────────────────── */
.card-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 16px;
}
.card-grid .card {
  flex-direction: column;
}
.card-grid .card-icon {
  margin-bottom: 8px;
}

.placeholder-card {
  opacity: 0.55;
}

.project-link {
  display: inline-block;
  margin-top: 8px;
  color: var(--accent);
  font-weight: 600;
  text-decoration: none;
  transition: color 0.2s;
}
.project-link:hover {
  color: var(--accent-hover);
}

.card-body h3 a {
  color: var(--accent);
  text-decoration: none;
  transition: color 0.2s;
}
.card-body h3 a:hover {
  color: var(--accent-hover);
  text-decoration: underline;
}

/* Detail page meta */
.detail-meta {
  margin-top: 16px;
  padding: 16px 20px;
  background: var(--bg-alt);
  border-radius: var(--radius);
  border: 1px solid var(--border);
  line-height: 1.8;
}
.detail-meta p {
  margin: 0;
}

/* Skill tags */
.skill-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-top: 8px;
}
.tag {
  display: inline-block;
  padding: 4px 12px;
  border-radius: 20px;
  background: var(--bg-alt);
  border: 1px solid var(--border);
  font-size: 0.85rem;
  color: var(--text);
  white-space: nowrap;
  transition:
    background 0.2s,
    border-color 0.2s;
}
.tag:hover {
  background: var(--accent);
  color: #fff;
  border-color: var(--accent);
}

/* ── Footer ─────────────────────────────────────────────── */
.site-footer {
  padding: 24px 0 20px;
  border-top: 1px solid var(--border);
  background: var(--bg);
  transition: background var(--transition);
}

.footer-inner {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 12px;
  text-align: center;
}

.footer-links {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 24px;
}

.footer-links a {
  display: flex;
  align-items: center;
  gap: 6px;
  font-size: 0.85rem;
  color: var(--text-muted);
  transition: color var(--transition);
}
.footer-links a:hover {
  color: var(--accent);
  text-decoration: none;
}

.footer-icon {
  width: 16px;
  height: 16px;
  flex-shrink: 0;
}

.footer-copy {
  font-size: 0.78rem;
  color: var(--text-muted);
}

/* ── Responsive ─────────────────────────────────────────── */
@media (max-width: 720px) {
  .hero-grid {
    grid-template-columns: 1fr;
  }
  .hero-photo {
    order: -1;
  }
  .photo-img {
    width: 160px;
    height: 200px;
  }

  .hero-name {
    font-size: 1.8rem;
  }
  .name-zh {
    font-size: 1.2rem;
  }

  .main-nav {
    display: none;
  }
  .site-title {
    flex: 1;
  }

  .card-grid {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 480px) {
  .header-inner {
    gap: 12px;
  }
  .hero {
    padding: 40px 0 36px;
  }
  .section {
    padding: 40px 0;
  }
  .footer-links {
    gap: 16px;
  }
}

/* ── Research / Publications ──────────────────────────── */
.section-subtitle {
  color: var(--text-muted);
  font-size: 0.95rem;
  margin-top: -8px;
  margin-bottom: 24px;
}
.section-subtitle a {
  color: var(--accent);
  text-decoration: none;
}
.section-subtitle a:hover {
  text-decoration: underline;
}

.publication-card .card-body h3 {
  font-size: 1.05rem;
  line-height: 1.45;
  margin-bottom: 6px;
}
.pub-authors {
  font-size: 0.9rem;
  color: var(--text);
  margin-bottom: 2px !important;
}
.pub-authors strong {
  color: var(--accent);
}
.pub-venue {
  font-size: 0.85rem;
  color: var(--text-muted);
  font-style: italic;
}

/* ── Publication Toggle ────────────────────────────────── */
.pub-toggle-btn {
  display: block;
  width: 100%;
  margin-top: 0;
  margin-bottom: 0;
  padding: 10px 20px;
  font-size: 0.9rem;
  font-family: var(--font-sans);
  color: var(--accent);
  background: transparent;
  border: 1px solid var(--accent);
  border-radius: 8px;
  cursor: pointer;
  text-align: center;
  transition:
    background var(--transition),
    color var(--transition);
}
.pub-toggle-btn:hover {
  background: var(--accent);
  color: #fff;
}

/* Collapsed state: hide the entire card */
.publication-card.collapsed {
  display: none;
}