/* ===== AiR Lab — Design tokens ===== */
:root {
  --color-bg: #ffffff;
  --color-bg-alt: #eaf3fc;
  --color-text: #10233d;
  --color-text-muted: #5c7291;
  --color-border: #d7e6f8;
  --color-accent: #2451e0;
  --color-accent-dark: #1a3aa8;
  --color-header-bg: rgba(240, 247, 253, 0.92);

  --font-base: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;

  --container-width: 1120px;
  --space-1: 8px;
  --space-2: 16px;
  --space-3: 24px;
  --space-4: 40px;
  --space-5: 64px;
  --space-6: 96px;
  --space-7: 140px;

  --radius: 10px;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  font-family: var(--font-base);
  color: var(--color-text);
  background: var(--color-bg);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}

a { color: inherit; text-decoration: none; }

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

.container {
  width: 100%;
  max-width: var(--container-width);
  margin: 0 auto;
  padding: 0 var(--space-3);
}

/* ===== Header ===== */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: var(--color-header-bg);
  backdrop-filter: saturate(180%) blur(12px);
  border-bottom: 1px solid var(--color-border);
}

.site-header .container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 72px;
}

.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  line-height: 1.15;
}

.brand-logo {
  height: 34px;
  width: auto;
}

.brand-sub {
  font-size: 0.7rem;
  color: var(--color-text-muted);
  letter-spacing: 0.02em;
}

.footer-logo {
  height: 28px;
  width: auto;
  margin-bottom: var(--space-2);
}

.nav {
  display: flex;
  align-items: center;
  gap: var(--space-4);
}

.nav-links {
  display: flex;
  gap: var(--space-3);
  list-style: none;
  margin: 0;
  padding: 0;
}

.nav-links a {
  font-size: 0.92rem;
  font-weight: 500;
  color: var(--color-text-muted);
  padding: 8px 2px;
  border-bottom: 2px solid transparent;
  transition: color 0.15s ease, border-color 0.15s ease;
}

.nav-links a:hover,
.nav-links a.active {
  color: var(--color-text);
  border-bottom-color: var(--color-accent);
}

.nav-toggle {
  display: none;
  background: none;
  border: none;
  cursor: pointer;
  padding: 8px;
}

.nav-toggle span {
  display: block;
  width: 22px;
  height: 2px;
  background: var(--color-text);
  margin: 5px 0;
}

/* ===== Hero ===== */
.hero {
  padding: var(--space-7) 0 var(--space-6);
  border-bottom: 1px solid var(--color-border);
  background-color: #eaf3fc;
}

.eyebrow {
  display: inline-block;
  font-size: 0.78rem;
  font-weight: 600;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--color-accent);
  margin-bottom: var(--space-2);
}

.hero h1 {
  font-size: clamp(2.4rem, 5vw, 3.6rem);
  line-height: 1.08;
  letter-spacing: -0.02em;
  margin: 0 0 var(--space-3);
  max-width: 16ch;
}

.hero-lede {
  font-size: 1.15rem;
  color: var(--color-text-muted);
  max-width: 58ch;
  margin: 0 0 var(--space-4);
}

.hero-meta {
  font-size: 0.95rem;
  color: var(--color-text-muted);
}

.btn-row {
  display: flex;
  gap: var(--space-2);
  margin-top: var(--space-4);
}

.btn {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 12px 22px;
  border-radius: 999px;
  font-size: 0.92rem;
  font-weight: 600;
  transition: transform 0.15s ease, background 0.15s ease;
}

.btn-primary {
  background: var(--color-text);
  color: #fff;
}

.btn-primary:hover { background: var(--color-accent-dark); }

.btn-secondary {
  background: transparent;
  color: var(--color-text);
  border: 1px solid var(--color-border);
}

.btn-secondary:hover { border-color: var(--color-text); }

/* ===== Section shell ===== */
.section {
  padding: var(--space-6) 0;
  border-bottom: 1px solid var(--color-border);
}

.section:last-of-type { border-bottom: none; }

.section-head {
  display: flex;
  align-items: flex-end;
  justify-content: space-between;
  gap: var(--space-3);
  margin-bottom: var(--space-5);
}

.section-head h2 {
  font-size: clamp(1.6rem, 3vw, 2.1rem);
  letter-spacing: -0.01em;
  margin: 0;
}

.section-head .section-note {
  color: var(--color-text-muted);
  font-size: 0.95rem;
  max-width: 42ch;
}

.section-link {
  font-size: 0.9rem;
  font-weight: 600;
  color: var(--color-accent);
  white-space: nowrap;
}

/* ===== Research cards (numbered, 3-4 col) ===== */
.research-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: var(--space-3);
}

.research-card {
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: var(--space-3);
  display: flex;
  flex-direction: column;
  min-height: 260px;
  transition: border-color 0.15s ease, transform 0.15s ease;
}

.research-card:hover {
  border-color: var(--color-accent);
  transform: translateY(-2px);
}

.research-card .num {
  font-size: 0.8rem;
  font-weight: 700;
  color: var(--color-text-muted);
  letter-spacing: 0.05em;
}

.research-card .icon {
  width: 44px;
  height: 44px;
  border-radius: 10px;
  margin: var(--space-2) 0 var(--space-2);
  background: linear-gradient(135deg, var(--color-accent), #6f8cff);
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
}

.research-card .icon svg {
  width: 24px;
  height: 24px;
  stroke: #fff;
  fill: none;
  stroke-width: 1.6;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.research-card h3 {
  font-size: 1.08rem;
  margin: 0 0 8px;
  letter-spacing: -0.01em;
}

.research-card p {
  font-size: 0.9rem;
  color: var(--color-text-muted);
  margin: 0 0 var(--space-2);
  flex-grow: 1;
}

.research-card .card-link {
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--color-accent);
}

/* ===== News list ===== */
.news-list {
  list-style: none;
  margin: 0;
  padding: 0;
  max-width: 760px;
  border-bottom: 1px solid var(--color-border);
}

.news-item {
  display: flex;
  gap: var(--space-3);
  padding: var(--space-2) 0;
  border-top: 1px solid var(--color-border);
}

.news-item.hidden { display: none; }

.news-toggle {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  margin-top: var(--space-3);
  background: transparent;
  border: none;
  color: var(--color-accent);
  font-size: 0.9rem;
  font-weight: 600;
  cursor: pointer;
  padding: 0;
}

.news-toggle:hover { color: var(--color-accent-dark); }

.news-toggle .count { color: var(--color-text-muted); font-weight: 500; }

.news-date {
  flex: 0 0 110px;
  font-size: 0.82rem;
  font-weight: 700;
  color: var(--color-accent);
  letter-spacing: 0.02em;
  padding-top: 2px;
}

.news-text { font-size: 0.96rem; }

/* ===== Footer / contact ===== */
.site-footer {
  padding: var(--space-5) 0 var(--space-4);
  background: var(--color-bg-alt);
}

.footer-grid {
  display: grid;
  grid-template-columns: 1.3fr 1fr;
  gap: var(--space-4);
  padding-bottom: var(--space-4);
  border-bottom: 1px solid var(--color-border);
}

.footer-grid h3 {
  font-size: 1rem;
  margin: 0 0 var(--space-2);
}

.footer-grid p {
  margin: 0 0 4px;
  font-size: 0.92rem;
  color: var(--color-text-muted);
}

.footer-grid a.email {
  color: var(--color-accent);
  font-weight: 600;
}

.footer-bottom {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding-top: var(--space-2);
  font-size: 0.8rem;
  color: var(--color-text-muted);
  flex-wrap: wrap;
  gap: 8px;
}

/* ===== Page header (interior pages) ===== */
.page-header {
  padding: var(--space-6) 0 var(--space-4);
  border-bottom: 1px solid var(--color-border);
}

.page-header h1 {
  font-size: clamp(2rem, 4vw, 2.7rem);
  letter-spacing: -0.02em;
  margin: 0 0 var(--space-2);
}

.page-header p {
  color: var(--color-text-muted);
  max-width: 60ch;
  font-size: 1.02rem;
  margin: 0;
}

/* ===== Professor bio page ===== */
.bio-top {
  display: grid;
  grid-template-columns: 140px 1fr;
  gap: var(--space-4);
  align-items: center;
}

.bio-avatar {
  width: 140px;
  height: 140px;
  border-radius: 50%;
  object-fit: cover;
  background: linear-gradient(135deg, var(--color-accent), #6f8cff);
}

.bio-role {
  color: var(--color-accent);
  font-weight: 600;
  margin: 4px 0 2px;
}

.bio-links {
  display: flex;
  gap: var(--space-2);
  margin-top: var(--space-3);
  flex-wrap: wrap;
}

.bio-section {
  padding: var(--space-5) 0;
  border-bottom: 1px solid var(--color-border);
}

.bio-section:last-child { border-bottom: none; }

.bio-section h2 {
  font-size: 1.3rem;
  margin: 0 0 var(--space-3);
}

.interest-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}

.timeline {
  list-style: none;
  margin: 0;
  padding: 0;
  max-width: 68ch;
}

.timeline li {
  display: grid;
  grid-template-columns: 110px 1fr;
  gap: var(--space-3);
  padding: 10px 0;
  border-top: 1px solid var(--color-border);
  font-size: 0.95rem;
}

.timeline li:last-child { padding-bottom: 0; }

.timeline .year {
  font-weight: 700;
  color: var(--color-accent);
  font-size: 0.88rem;
}

/* ===== Members ===== */
.member-group { padding: var(--space-5) 0; border-bottom: 1px solid var(--color-border); }
.member-group:last-child { border-bottom: none; }

.member-group-title {
  display: flex;
  align-items: baseline;
  gap: var(--space-2);
  margin-bottom: var(--space-3);
}

.member-group-title h2 {
  font-size: 1.3rem;
  margin: 0;
}

.member-group-title .count {
  font-size: 0.85rem;
  color: var(--color-text-muted);
}

.pi-card {
  display: grid;
  grid-template-columns: 120px 1fr;
  gap: var(--space-3);
  align-items: center;
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: var(--space-3);
}

.pi-card-link {
  transition: border-color 0.15s ease, transform 0.15s ease;
}

.pi-card-link:hover {
  border-color: var(--color-accent);
  transform: translateY(-2px);
}

.pi-avatar {
  width: 100px;
  height: 100px;
  border-radius: 50%;
  object-fit: cover;
  background: linear-gradient(135deg, var(--color-accent), #6f8cff);
}

.pi-card h3 { margin: 0 0 4px; font-size: 1.2rem; }
.pi-card .role { color: var(--color-accent); font-weight: 600; font-size: 0.85rem; margin-bottom: 8px; }
.pi-card p { margin: 2px 0; font-size: 0.9rem; color: var(--color-text-muted); }

.member-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--space-2);
}

.member-card {
  position: relative;
  display: flex;
  align-items: center;
  gap: var(--space-3);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: var(--space-3);
}

.member-link {
  position: absolute;
  top: 10px;
  right: 10px;
  width: 22px;
  height: 22px;
  color: var(--color-text-muted);
  transition: color 0.15s ease;
}

.member-link:hover { color: var(--color-accent); }

.member-link svg { width: 100%; height: 100%; }

.member-link.member-link-home { right: 36px; }

.member-avatar {
  width: 100px;
  height: 100px;
  border-radius: 50%;
  object-fit: cover;
  flex-shrink: 0;
  background: var(--color-bg-alt);
}

.member-card h4 {
  margin: 0 0 6px;
  font-size: 1rem;
}

.tag {
  display: inline-block;
  font-size: 0.72rem;
  font-weight: 600;
  color: var(--color-accent);
  background: rgba(36, 81, 224, 0.08);
  padding: 3px 9px;
  border-radius: 999px;
  margin-bottom: 8px;
}

.member-card .email {
  font-size: 0.82rem;
  color: var(--color-text-muted);
  word-break: break-all;
}

/* ===== Research detail sections ===== */
.research-detail {
  padding: var(--space-6) 0;
  border-bottom: 1px solid var(--color-border);
}

.research-detail:last-child { border-bottom: none; }

.research-detail-head {
  display: grid;
  grid-template-columns: 90px 1fr;
  gap: var(--space-3);
  margin-bottom: var(--space-3);
}

.big-num {
  font-size: 2.2rem;
  font-weight: 700;
  color: var(--color-border);
  line-height: 1;
}

.research-detail h2 {
  font-size: 1.6rem;
  margin: 0 0 var(--space-1);
  letter-spacing: -0.01em;
}

.research-detail .desc {
  color: var(--color-text-muted);
  max-width: 68ch;
  margin: 0 0 var(--space-3);
}

.related-pubs {
  list-style: none;
  margin: 0;
  padding: 0;
  max-width: 68ch;
}

.related-pubs li {
  font-size: 0.9rem;
  padding: 6px 0;
  border-top: 1px dashed var(--color-border);
}

.topic-block {
  padding: var(--space-4) 0;
  border-top: 1px solid var(--color-border);
}

.topic-block:first-of-type { border-top: none; padding-top: var(--space-1); }

.topic-block h3 {
  font-size: 1.15rem;
  margin: 0 0 8px;
  letter-spacing: -0.01em;
}

.topic-highlight {
  display: inline-block;
  font-size: 0.78rem;
  font-weight: 600;
  color: var(--color-accent-dark);
  background: rgba(36, 81, 224, 0.08);
  padding: 4px 10px;
  border-radius: 999px;
  margin-bottom: 10px;
}

.topic-block .desc-list {
  margin: 0 0 10px;
  padding-left: 1.15em;
  color: var(--color-text-muted);
  font-size: 0.92rem;
  max-width: 68ch;
}

.topic-block .desc-list li { margin-bottom: 4px; }

.topic-block .desc { margin: 0 0 10px; }

.research-figure-row {
  display: flex;
  gap: var(--space-2);
  flex-wrap: wrap;
  margin: 14px 0;
}

.research-figure {
  margin: 14px 0;
  flex: 1 1 220px;
}

.research-figure-row .research-figure { margin: 0; }

.research-figure img,
.research-figure video {
  width: 100%;
  display: block;
  border-radius: var(--radius);
  border: 1px solid var(--color-border);
}

.research-figure figcaption {
  font-size: 0.8rem;
  color: var(--color-text-muted);
  margin-top: 6px;
}

.video-row {
  display: flex;
  gap: var(--space-2);
  flex-wrap: wrap;
  align-items: stretch;
  margin: 14px 0;
}

.video-row video {
  height: 320px;
  width: auto;
  max-width: 100%;
  flex: 1 1 auto;
  object-fit: cover;
  border-radius: var(--radius);
  border: 1px solid var(--color-border);
}

.watch-link {
  display: inline-block;
  margin-top: 2px;
  margin-bottom: 10px;
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--color-accent);
  cursor: pointer;
}

.video-embed {
  position: relative;
  width: 100%;
  height: 0;
  padding-top: 56.25%;
  margin: 0 0 14px;
  border-radius: var(--radius);
  border: 1px solid var(--color-border);
  overflow: hidden;
}

.video-embed iframe {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  border: 0;
}

/* ===== Research topic hero (detail pages) ===== */
.topic-hero-img {
  width: 100%;
  max-height: 420px;
  object-fit: contain;
  background: var(--color-bg-alt);
  border-radius: var(--radius);
  border: 1px solid var(--color-border);
  margin-top: var(--space-4);
}

/* ===== Research summary cards (research.html) ===== */
.research-summary-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: var(--space-3);
}

.research-summary-card {
  display: flex;
  flex-direction: column;
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  overflow: hidden;
  transition: border-color 0.15s ease, transform 0.15s ease;
}

.research-summary-card:hover {
  border-color: var(--color-accent);
  transform: translateY(-2px);
}

.research-summary-card img {
  width: 100%;
  aspect-ratio: 16 / 9;
  object-fit: cover;
  display: block;
  border-bottom: 1px solid var(--color-border);
}

.research-summary-card .body { padding: var(--space-3); }

.research-summary-card .num {
  font-size: 0.8rem;
  font-weight: 700;
  color: var(--color-text-muted);
  letter-spacing: 0.05em;
}

.research-summary-card h2 {
  font-size: 1.25rem;
  margin: 6px 0 8px;
  letter-spacing: -0.01em;
}

.research-summary-card p {
  font-size: 0.92rem;
  color: var(--color-text-muted);
  margin: 0 0 var(--space-2);
}

.summary-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  margin-bottom: var(--space-2);
}

.summary-tags span {
  font-size: 0.72rem;
  font-weight: 600;
  color: var(--color-text-muted);
  background: var(--color-bg-alt);
  padding: 3px 9px;
  border-radius: 999px;
}

.back-to-top {
  display: inline-block;
  margin-top: var(--space-3);
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--color-accent);
}

/* ===== Publications ===== */
.pub-year {
  margin-bottom: var(--space-5);
}

.pub-year h2 {
  font-size: 1.5rem;
  margin: 0 0 var(--space-2);
  color: var(--color-accent);
}

.pub-list {
  list-style: none;
  margin: 0;
  padding: 0;
}

.pub-item {
  padding: var(--space-2) 0;
  border-top: 1px solid var(--color-border);
}

.pub-item .pub-title {
  font-weight: 600;
  font-size: 1rem;
  margin-bottom: 4px;
}

.pub-item .pub-authors {
  font-size: 0.88rem;
  color: var(--color-text-muted);
  margin-bottom: 2px;
}

.pub-item .pub-venue {
  font-size: 0.85rem;
  color: var(--color-text);
}

.pub-links {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  margin-top: 8px;
}

.pub-link {
  font-size: 0.78rem;
  font-weight: 600;
  color: var(--color-accent);
  border: 1px solid var(--color-border);
  padding: 3px 10px;
  border-radius: 999px;
  transition: border-color 0.15s ease, background 0.15s ease;
}

.pub-link:hover {
  border-color: var(--color-accent);
  background: rgba(36, 81, 224, 0.06);
}

.badge {
  display: inline-block;
  font-size: 0.7rem;
  font-weight: 700;
  color: var(--color-accent-dark);
  background: rgba(36, 81, 224, 0.1);
  padding: 2px 8px;
  border-radius: 999px;
  margin-left: 6px;
  vertical-align: middle;
}

/* ===== Projects ===== */
.project-group {
  padding: var(--space-5) 0;
  border-bottom: 1px solid var(--color-border);
}

.project-group:last-child { border-bottom: none; }

.project-group-title {
  display: flex;
  align-items: baseline;
  gap: var(--space-2);
  margin-bottom: var(--space-3);
}

.project-group-title h2 {
  font-size: 1.3rem;
  margin: 0;
}

.project-group-title .count {
  font-size: 0.85rem;
  color: var(--color-text-muted);
}

.project-list {
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
}

.project-card {
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: var(--space-3);
  transition: border-color 0.15s ease;
}

.project-card:hover { border-color: var(--color-accent); }

.project-title-row {
  display: flex;
  align-items: center;
  gap: 8px;
  flex-wrap: wrap;
  margin-bottom: 4px;
}

.project-title-row h3 {
  font-size: 1.05rem;
  margin: 0;
  letter-spacing: -0.01em;
}

.role-tag {
  font-size: 0.68rem;
  font-weight: 700;
  letter-spacing: 0.03em;
  padding: 2px 8px;
  border-radius: 999px;
  background: var(--color-bg-alt);
  color: var(--color-text-muted);
  border: 1px solid var(--color-border);
  flex-shrink: 0;
}

.role-tag.pi {
  color: var(--color-accent-dark);
  background: rgba(36, 81, 224, 0.08);
  border-color: transparent;
}

.project-meta {
  font-size: 0.86rem;
  color: var(--color-text-muted);
  margin: 0 0 10px;
}

.status-badge {
  display: inline-block;
  font-size: 0.72rem;
  font-weight: 700;
  padding: 3px 10px;
  border-radius: 999px;
  flex-shrink: 0;
}

.status-badge.active {
  color: var(--color-accent-dark);
  background: rgba(36, 81, 224, 0.1);
}

.status-badge.done {
  color: #1a3aa8;
  background: rgba(16, 35, 61, 0.08);
}

.project-desc {
  font-size: 0.92rem;
  color: var(--color-text-muted);
  margin: 0;
}

/* ===== Responsive ===== */
@media (max-width: 860px) {
  .research-grid { grid-template-columns: repeat(2, 1fr); }
  .member-grid { grid-template-columns: repeat(2, 1fr); }
  .footer-grid { grid-template-columns: 1fr; }
}

@media (max-width: 640px) {
  .nav-links {
    position: absolute;
    top: 72px;
    left: 0;
    right: 0;
    background: var(--color-bg);
    flex-direction: column;
    gap: 0;
    border-bottom: 1px solid var(--color-border);
    display: none;
  }
  .nav-links.open { display: flex; }
  .nav-links a { padding: 14px var(--space-3); width: 100%; border-bottom: 1px solid var(--color-border); }
  .nav-toggle { display: block; }
  .research-grid { grid-template-columns: 1fr; }
  .research-summary-grid { grid-template-columns: 1fr; }
  .member-grid { grid-template-columns: 1fr; }
  .pi-card { grid-template-columns: 1fr; text-align: center; }
  .pi-avatar { margin: 0 auto; }
  .research-detail-head { grid-template-columns: 1fr; }
  .bio-top { grid-template-columns: 1fr; text-align: center; }
  .bio-avatar { margin: 0 auto; }
  .bio-links { justify-content: center; }
  .timeline li { grid-template-columns: 1fr; gap: 2px; }
}