/* ===== QCL Dark Emerald Theme (default) ===== */

:root {
  --bg: #080c10;
  --card-bg: #0c1218;
  --border: #1a2530;
  --border-hover: #2a4a3a;
  --accent: #4adeaa;
  --accent-hover: #3cc898;
  --text: #c8d0d8;
  --text-secondary: #6a7a72;
  --text-title: #d0ddd5;
  --text-heading: #e0e8e4;
  --text-dim: #445;
  --nav-bg: rgba(8, 12, 16, 0.95);
  --nav-link: #889;
  --tag-bg: #0a1a14;
  --tag-color: #4a6a5a;
  --tag-border: #1a3a2a;
  --code-bg: #1a2530;
  --input-bg: #0a0e14;
  --avatar-bg: #1a2530;
  --avatar-border: #2a3a30;
  --error-bg: #1a1014;
  --error-border: #3a1a2a;
  --error-color: #e06060;
  --dropdown-shadow: rgba(0,0,0,0.4);
  --hero-overlay-top: rgba(8,12,16,0.55);
  --hero-overlay-bottom: rgba(8,12,16,0.82);
}

/* ===== Classic Academic White Theme ===== */
[data-theme="light"] {
  --bg: #ffffff;
  --card-bg: #f7f8fa;
  --border: #e0e4e8;
  --border-hover: #b0c4b8;
  --accent: #1a8a5a;
  --accent-hover: #14704a;
  --text: #3a4048;
  --text-secondary: #6a7580;
  --text-title: #1a2030;
  --text-heading: #0a1520;
  --text-dim: #99a0a8;
  --nav-bg: rgba(255, 255, 255, 0.95);
  --nav-link: #555d68;
  --tag-bg: #eef6f2;
  --tag-color: #2a6a4a;
  --tag-border: #c0dcd0;
  --code-bg: #f0f2f5;
  --input-bg: #f5f6f8;
  --avatar-bg: #eef0f2;
  --avatar-border: #d0d8dc;
  --error-bg: #fef2f2;
  --error-border: #fca5a5;
  --error-color: #dc2626;
  --dropdown-shadow: rgba(0,0,0,0.1);
  --hero-overlay-top: rgba(0,0,0,0.35);
  --hero-overlay-bottom: rgba(0,0,0,0.6);
}

/* Theme transition */
body, .nav, .news-item, .research-card, .team-card, .paper-item,
.join-contact, .alumni-item {
  transition: background-color 0.3s, color 0.3s, border-color 0.3s;
}

/* ===== Reset & Base ===== */
*, *::before, *::after { margin: 0; padding: 0; box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  background: var(--bg);
  color: var(--text);
  font-family: -apple-system, 'Segoe UI', Roboto, 'Helvetica Neue', sans-serif;
  font-size: 34px;
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}
.skip-link {
  position: absolute; top: -100%; left: 0;
  background: var(--accent); color: #080c10;
  padding: 8px 16px; z-index: 1000; font-size: 14px;
}
.skip-link:focus { top: 0; }
a { color: var(--accent); text-decoration: none; transition: color 0.2s; }
a:hover { color: var(--accent-hover); }
img { max-width: 100%; height: auto; }

/* ===== Navigation ===== */
.nav {
  position: sticky; top: 0; z-index: 100;
  background: var(--nav-bg);
  -webkit-backdrop-filter: blur(14px);
  backdrop-filter: blur(14px);
  border-bottom: 1px solid var(--border);
  padding: 0 56px;
  display: flex; justify-content: space-between; align-items: center;
  height: 80px;
}
.nav-logo {
  font-size: 36px; font-weight: 800;
  color: var(--accent); letter-spacing: 5px; text-decoration: none;
}
.nav-logo:hover { color: var(--accent); }
.nav-logo span {
  font-size: 15px; color: var(--text-secondary); font-weight: 400;
  letter-spacing: 2px; margin-left: 14px;
}
.nav-links { display: flex; gap: 8px; align-items: center; }
.nav-item { position: relative; }
.nav-item > a {
  color: var(--nav-link); font-size: 17px; text-decoration: none;
  padding: 8px 16px; display: block;
  border-bottom: 2px solid transparent;
  transition: color 0.2s, border-color 0.2s;
}
.nav-item > a:hover, .nav-item > a.active { color: var(--accent); border-bottom-color: var(--accent); }

/* Dropdown */
.nav-dropdown {
  display: none; position: absolute; top: 100%; left: 0;
  background: var(--nav-bg); -webkit-backdrop-filter: blur(14px); backdrop-filter: blur(14px);
  border: 1px solid var(--border); border-radius: 8px;
  min-width: 200px; padding: 8px 0;
  box-shadow: 0 8px 32px var(--dropdown-shadow);
  z-index: 200;
}
.nav-item:hover .nav-dropdown,
.nav-item:focus-within .nav-dropdown { display: block; }
.nav-dropdown a {
  display: block; padding: 10px 20px;
  color: var(--nav-link); font-size: 14px;
}
.nav-dropdown a:hover { color: var(--accent); background: rgba(74,222,170,0.05); }

/* Language toggle */
.lang-toggle {
  color: var(--nav-link); font-size: 14px; font-weight: 600;
  padding: 4px 12px; border: 1px solid var(--border); border-radius: 4px;
  margin-left: 16px; text-decoration: none;
}
.lang-toggle:hover { color: var(--accent); border-color: var(--accent); }

/* Mobile hamburger */
.menu-toggle { display: none; background: none; border: none; cursor: pointer; padding: 8px; }
.menu-toggle span { display: block; width: 24px; height: 2px; background: var(--text); margin: 6px 0; transition: 0.3s; }

/* Theme toggle */
.theme-toggle {
  background: none; border: 1px solid var(--border); border-radius: 4px;
  cursor: pointer; padding: 4px 10px; margin-left: 8px;
  font-size: 16px; line-height: 1; color: var(--nav-link);
  transition: border-color 0.2s;
}
.theme-toggle:hover { border-color: var(--accent); }

/* ===== Hero ===== */
.hero {
  position: relative; height: 620px; overflow: hidden;
  display: flex; align-items: center; justify-content: center;
}
.hero-bg {
  position: absolute; inset: 0;
  background: url('../img/hero-bg.jpg') center/cover no-repeat;
}
.hero-bg::after {
  content: ''; position: absolute; inset: 0;
  background: linear-gradient(180deg, var(--hero-overlay-top) 0%, var(--hero-overlay-bottom) 100%);
}
.hero-content { position: relative; z-index: 2; text-align: center; }
.hero-title {
  font-size: 100px; font-weight: 800; color: #fff;
  letter-spacing: 16px; text-shadow: 0 0 80px rgba(74,222,170,0.15);
}
.hero-subtitle { font-size: 30px; color: #d0e8dc; margin-top: 16px; letter-spacing: 8px; font-weight: 300; text-shadow: 0 2px 12px rgba(0,0,0,0.5); }
.hero-subtitle-en { font-size: 18px; color: #a0c0b0; margin-top: 8px; letter-spacing: 4px; text-shadow: 0 2px 8px rgba(0,0,0,0.5); }
.hero-affiliation { font-size: 14px; color: #90b0a0; margin-top: 10px; letter-spacing: 2px; text-shadow: 0 2px 8px rgba(0,0,0,0.4); }
.hero-divider {
  width: 100px; height: 2px; margin: 28px auto;
  background: linear-gradient(90deg, transparent, var(--accent), transparent);
}
.hero-desc { font-size: 18px; color: #c0d8cc; max-width: 520px; margin: 0 auto; line-height: 1.8; text-shadow: 0 2px 8px rgba(0,0,0,0.4); }

/* ===== Container & Sections ===== */
.container { max-width: 1000px; margin: 0 auto; padding: 48px 40px; }
.section { margin-bottom: 56px; }
.section-title {
  font-size: 28px; font-weight: 700; color: var(--text-heading);
  margin-bottom: 32px; padding-bottom: 12px;
  border-bottom: 1px solid var(--border);
}
.section-title::before {
  content: ''; display: inline-block; width: 4px; height: 24px;
  background: var(--accent); margin-right: 14px;
  vertical-align: middle; border-radius: 2px;
}
.page-title { font-size: 36px; font-weight: 700; color: var(--text-heading); margin-bottom: 12px; }
.page-subtitle { font-size: 16px; color: var(--text-secondary); margin-bottom: 48px; }

/* ===== News Cards ===== */
.news-list { display: flex; flex-direction: column; gap: 24px; }
.news-item {
  background: var(--card-bg); border: 1px solid var(--border);
  border-radius: 8px; padding: 28px 32px; transition: border-color 0.2s;
}
.news-item:hover { border-color: var(--border-hover); }
.news-meta { display: flex; align-items: center; gap: 12px; margin-bottom: 10px; }
.news-date { font-size: 14px; color: var(--accent); }
.news-tag {
  font-size: 11px; color: var(--tag-color); background: var(--tag-bg);
  padding: 3px 10px; border-radius: 10px; border: 1px solid var(--tag-border);
}
.news-title { font-size: 22px; font-weight: 600; color: var(--text-title); margin-bottom: 12px; line-height: 1.4; }
.news-title a { color: inherit; text-decoration: none; }
.news-title a:hover { color: var(--accent); }
.news-excerpt { font-size: 15px; color: var(--text-secondary); line-height: 1.8; }
.news-readmore { display: inline-block; margin-top: 14px; font-size: 14px; color: var(--accent); }

/* ===== Research Cards ===== */
.research-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 32px; }
.research-card {
  background: var(--card-bg); border: 1px solid var(--border);
  border-radius: 8px; overflow: hidden; transition: border-color 0.2s;
  text-decoration: none; display: block;
}
.research-card:hover { border-color: var(--border-hover); }
.research-card-img { width: 100%; height: 160px; overflow: hidden; }
.research-card-img img { width: 100%; height: 100%; object-fit: cover; transition: transform 0.3s; }
.research-card:hover .research-card-img img { transform: scale(1.05); }
.research-card-body { padding: 20px 24px; }
.research-card h4 { font-size: 18px; color: var(--accent); margin-bottom: 10px; }
.research-card p { font-size: 14px; color: var(--text-secondary); line-height: 1.7; }

/* ===== Research Detail ===== */
.research-header { display: flex; align-items: center; gap: 14px; margin-bottom: 16px; }
.research-icon { font-size: 32px; }
.research-detail-title { font-size: 30px; font-weight: 700; color: var(--accent); }
.research-desc { font-size: 15px; color: var(--text-secondary); line-height: 1.8; margin-bottom: 32px; max-width: 800px; }
.research-img {
  width: 100%; max-height: 300px; object-fit: cover;
  border-radius: 8px; margin-bottom: 32px; border: 1px solid var(--border);
}
.papers-heading {
  font-size: 16px; color: var(--text-secondary); text-transform: uppercase;
  letter-spacing: 2px; margin-bottom: 16px; padding-bottom: 8px;
  border-bottom: 1px solid var(--border);
}
.paper-list { display: flex; flex-direction: column; gap: 12px; }
.paper-item {
  background: var(--card-bg); border: 1px solid var(--border);
  border-radius: 6px; padding: 16px 20px; transition: border-color 0.2s;
}
.paper-item:hover { border-color: var(--border-hover); }
.paper-title { font-size: 15px; font-weight: 600; color: var(--text-title); margin-bottom: 6px; line-height: 1.4; }
.paper-meta { font-size: 13px; color: var(--text-secondary); }
.paper-meta .journal { color: var(--accent); }
.paper-links { margin-top: 6px; }
.paper-links a {
  font-size: 12px; color: var(--accent); margin-right: 12px;
  padding: 2px 8px; border: 1px solid var(--tag-border); border-radius: 4px;
}
.paper-links a:hover { color: var(--accent-hover); border-color: var(--accent); }

/* ===== Team ===== */
.team-section { margin-bottom: 48px; }
.team-section-title {
  font-size: 22px; font-weight: 600; color: var(--text-heading);
  margin-bottom: 20px; padding-bottom: 8px;
  border-bottom: 1px solid var(--border);
}
.team-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 24px; }
.team-card {
  background: var(--card-bg); border: 1px solid var(--border);
  border-radius: 8px; padding: 24px; text-align: center;
  transition: border-color 0.2s; text-decoration: none; display: block;
}
.team-card:hover { border-color: var(--border-hover); }
.team-avatar {
  width: 110px; height: 110px; border-radius: 50%; background: var(--avatar-bg);
  margin: 0 auto 16px; display: flex; align-items: center; justify-content: center;
  font-size: 36px; color: var(--accent); border: 2px solid var(--avatar-border);
  overflow: hidden;
}
.team-avatar img { width: 100%; height: 100%; object-fit: cover; }
.team-name { font-size: 18px; font-weight: 600; color: var(--text-title); }
.team-role { font-size: 13px; color: var(--accent); margin-top: 4px; }
.team-research { font-size: 13px; color: var(--text-secondary); margin-top: 8px; }
.team-bio { font-size: 12px; color: var(--text-secondary); margin-top: 8px; line-height: 1.6; }
.team-year { font-size: 12px; color: var(--text-dim); margin-top: 4px; }

/* Alumni list */
.alumni-list { display: flex; flex-direction: column; gap: 8px; }
.alumni-item {
  display: flex; justify-content: space-between; align-items: center;
  padding: 12px 16px; background: var(--card-bg);
  border: 1px solid var(--border); border-radius: 6px;
}
.alumni-name { font-size: 15px; color: var(--text-title); }
.alumni-role { font-size: 13px; color: var(--text-secondary); margin-left: 12px; }
.alumni-destination { font-size: 13px; color: var(--accent); }

/* ===== Join Page ===== */
.join-tier {
  margin-bottom: 48px; padding-bottom: 48px;
  border-bottom: 1px solid var(--border);
}
.join-tier:last-child { border-bottom: none; }
.join-tier-title { font-size: 24px; font-weight: 700; color: var(--accent); margin-bottom: 24px; }
.join-subtitle { font-size: 16px; font-weight: 600; color: var(--text-heading); margin-bottom: 12px; }
.join-list { list-style: none; padding: 0; }
.join-list li {
  padding: 8px 0; padding-left: 20px; position: relative;
  font-size: 14px; color: var(--text-secondary); line-height: 1.6;
}
.join-list li::before {
  content: ''; position: absolute; left: 0; top: 16px;
  width: 6px; height: 6px; border-radius: 50%; background: var(--accent);
}
.join-contact {
  background: var(--card-bg); border: 1px solid var(--border);
  border-radius: 8px; padding: 28px 32px; margin-top: 32px;
}
.join-contact h3 { font-size: 20px; color: var(--text-heading); margin-bottom: 16px; }
.join-contact p { font-size: 14px; color: var(--text-secondary); line-height: 1.8; }
.join-highlight { font-size: 15px; color: var(--accent); margin-bottom: 20px; font-weight: 600; }

/* ===== Footer ===== */
.footer {
  border-top: 1px solid var(--border);
  padding: 40px 56px; text-align: center; margin-top: 60px;
}
.footer-text { font-size: 14px; color: var(--text-dim); }
.footer-links { display: inline-block; margin-top: 10px; }
.footer-links a { color: var(--accent); margin: 0 4px; font-size: 13px; }
.footer-links span { color: var(--text-dim); font-size: 13px; }
.footer-sep { color: var(--text-dim); margin: 0 2px; }

/* ===== Post Detail ===== */
.post-header { margin-bottom: 32px; }
.post-title { font-size: 28px; font-weight: 700; color: var(--text-heading); line-height: 1.4; }
.post-meta { font-size: 14px; color: var(--text-secondary); margin-top: 12px; }
.post-meta .post-tag { color: var(--accent); }
.post-content { font-size: 15px; line-height: 1.8; color: var(--text); }
.post-content h2 { font-size: 22px; color: var(--text-heading); margin: 28px 0 16px; }
.post-content h3 { font-size: 18px; color: var(--text-title); margin: 24px 0 12px; }
.post-content p { margin-bottom: 16px; }
.post-content ul, .post-content ol { margin: 16px 0; padding-left: 24px; }
.post-content li { margin-bottom: 8px; }
.post-content code { background: var(--code-bg); padding: 2px 6px; border-radius: 3px; font-size: 13px; }

/* ===== 404 ===== */
.page-404 {
  display: flex; align-items: center; justify-content: center;
  min-height: calc(100vh - 80px); text-align: center;
}
.page-404 h1 { font-size: 72px; color: var(--accent); margin-bottom: 16px; }
.page-404 p { font-size: 18px; color: var(--text-secondary); margin-bottom: 24px; }

/* ===== Back link ===== */
.back-link { display: inline-block; font-size: 14px; color: var(--accent); margin-bottom: 24px; }

/* ===== Responsive ===== */
@media (max-width: 768px) {
  .nav { padding: 0 20px; height: 64px; }
  .nav-logo { font-size: 28px; }
  .nav-logo span { display: none; }
  .nav-links { display: none; flex-direction: column; position: absolute; top: 64px; left: 0; right: 0; background: var(--nav-bg); border-bottom: 1px solid var(--border); padding: 16px 0; }
  .nav-links.open { display: flex; }
  .nav-item > a { padding: 12px 24px; }
  .nav-dropdown { position: static; border: none; box-shadow: none; padding-left: 24px; display: none; }
  .nav-item.open .nav-dropdown { display: block; }
  .menu-toggle { display: block; }
  .lang-toggle { margin: 8px 24px; display: inline-block; }

  .hero { height: 400px; }
  .hero-title { font-size: 56px; letter-spacing: 8px; }
  .hero-subtitle { font-size: 20px; letter-spacing: 4px; }
  .hero-subtitle-en { font-size: 14px; }
  .hero-affiliation { font-size: 12px; }
  .hero-desc { font-size: 15px; }

  .container { padding: 32px 20px; }
  .research-grid { grid-template-columns: 1fr; }
  .team-grid { grid-template-columns: 1fr; }
  .page-title { font-size: 28px; }
  .section-title { font-size: 22px; }

  .login-box { width: 90%; padding: 32px 24px; }}