/* ============================================
   Ollie Liu — Personal Website
   Minimal, monochromatic design
   ============================================ */

/* ---------- CSS Variables (Light) ---------- */
:root {
  --bg: #fafafa;
  --bg-alt: #f0f0f0;
  --fg: #1a1a1a;
  --fg-muted: #666;
  --fg-faint: #999;
  --border: #e0e0e0;
  --accent: #1a1a1a;
  --accent-hover: #444;
  --tag-bg: #e8e8e8;
  --tag-fg: #333;
  --tag-preprint-bg: #f5f5f5;
  --tag-preprint-fg: #777;
  --featured-bg: #1a1a1a;
  --featured-fg: #fff;
  --card-bg: #fff;
  --card-featured-bg: rgba(255, 160, 50, 0.08);
  --card-featured-border: rgba(255, 160, 50, 0.25);
  --card-shadow: 0 1px 3px rgba(0,0,0,0.06);
  --nav-bg: rgba(250,250,250,0.92);
  --radius: 6px;
  --font-sans: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Inter', Helvetica, Arial, sans-serif;
  --font-mono: 'SFMono-Regular', 'Fira Code', 'Consolas', monospace;
  --transition: 0.2s ease;
  --max-width: 780px;
}

/* ---------- Dark mode ---------- */
[data-theme="dark"] {
  --bg: #111;
  --bg-alt: #1a1a1a;
  --fg: #e0e0e0;
  --fg-muted: #aaa;
  --fg-faint: #777;
  --border: #2a2a2a;
  --accent: #e0e0e0;
  --accent-hover: #ccc;
  --tag-bg: #2a2a2a;
  --tag-fg: #ccc;
  --tag-preprint-bg: #222;
  --tag-preprint-fg: #999;
  --featured-bg: #e0e0e0;
  --featured-fg: #111;
  --card-bg: #1a1a1a;
  --card-featured-bg: rgba(255, 160, 50, 0.1);
  --card-featured-border: rgba(255, 160, 50, 0.2);
  --card-shadow: 0 1px 3px rgba(0,0,0,0.3);
  --nav-bg: rgba(17,17,17,0.92);
}

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

html {
  scroll-behavior: smooth;
  scroll-padding-top: 72px;
}

body {
  font-family: var(--font-sans);
  background: var(--bg);
  color: var(--fg);
  line-height: 1.65;
  font-size: 15px;
  transition: background var(--transition), color var(--transition);
}

a {
  color: var(--fg);
  text-decoration: none;
  transition: color var(--transition);
}

a:hover {
  color: var(--accent-hover);
}

::selection {
  background: var(--accent);
  color: var(--bg);
}

/* ---------- Container ---------- */
.container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 24px;
}

/* ---------- Navigation ---------- */
#nav {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 100;
  background: var(--nav-bg);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border);
  transition: background var(--transition), border-color var(--transition);
}

.nav-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 24px;
  height: 56px;
  display: flex;
  align-items: center;
  gap: 24px;
}

.nav-name {
  font-weight: 700;
  font-size: 16px;
  letter-spacing: -0.02em;
  white-space: nowrap;
}

.nav-links {
  display: flex;
  gap: 20px;
  margin-left: auto;
  font-size: 13px;
}

.nav-links a {
  color: var(--fg-muted);
  transition: color var(--transition);
}

.nav-links a:hover {
  color: var(--fg);
}

#theme-toggle {
  background: none;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 6px;
  cursor: pointer;
  color: var(--fg-muted);
  display: flex;
  align-items: center;
  justify-content: center;
  transition: color var(--transition), border-color var(--transition);
}

#theme-toggle:hover {
  color: var(--fg);
  border-color: var(--fg-muted);
}

/* ---------- Hero ---------- */
#hero {
  padding: 120px 0 24px;
}

.hero-card {
  display: flex;
  gap: 32px;
  align-items: center;
}

.hero-photo {
  flex-shrink: 0;
  width: 150px;
}

.hero-photo img {
  width: 100%;
  border-radius: var(--radius);
  filter: grayscale(20%);
  transition: filter var(--transition);
}

.hero-photo img:hover {
  filter: grayscale(0%);
}

.hero-info {
  flex: 1;
  min-width: 0;
}

.hero-title {
  font-size: 15px;
  color: var(--fg-muted);
  margin-bottom: 4px;
}

.hero-role {
  font-size: 15px;
  color: var(--fg);
  margin-bottom: 14px;
}

.hero-role a {
  text-decoration: underline;
  text-underline-offset: 2px;
  text-decoration-color: var(--fg-faint);
}

.hero-role a:hover {
  text-decoration-color: var(--fg);
}

.hero-divider {
  border: none;
  border-top: 1px solid var(--border);
  margin: 32px 0;
}

.tagline {
  font-size: 15px;
  line-height: 1.7;
  margin-bottom: 0;
  color: var(--fg);
}

.tagline p {
  margin-bottom: 12px;
}

.tagline p:last-child {
  margin-bottom: 0;
}

.tagline a {
  text-decoration: underline;
  text-underline-offset: 2px;
  text-decoration-color: var(--fg-faint);
}

.tagline a:hover {
  text-decoration-color: var(--fg);
}

.hero-links {
  display: flex;
  gap: 10px;
  flex-wrap: wrap;
}

.btn {
  display: inline-block;
  padding: 8px 18px;
  font-size: 13px;
  font-weight: 500;
  border-radius: var(--radius);
  background: var(--accent);
  color: var(--bg);
  border: 1px solid var(--accent);
  transition: all var(--transition);
  cursor: pointer;
}

.btn:hover {
  opacity: 0.85;
  color: var(--bg);
}

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

.btn-outline:hover {
  border-color: var(--fg-muted);
  color: var(--fg);
}

.btn-icon {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 7px;
  line-height: 0;
}

.btn-icon svg {
  display: block;
}

/* ---------- Sections ---------- */
.section {
  padding: 0 0 48px;
}

.section h2 {
  font-size: 22px;
  font-weight: 700;
  letter-spacing: -0.03em;
  margin-bottom: 32px;
  padding-top: 48px;
  border-top: 1px solid var(--border);
}

/* ---------- Timeline ---------- */
.timeline {
  display: flex;
  flex-direction: column;
  gap: 28px;
}

.timeline-item {
  display: grid;
  grid-template-columns: 140px 1fr;
  gap: 24px;
}

.timeline-date {
  font-size: 13px;
  color: var(--fg-faint);
  font-variant-numeric: tabular-nums;
  padding-top: 2px;
}

.timeline-content h3 {
  font-size: 15px;
  font-weight: 600;
  margin-bottom: 2px;
}

.timeline-content p {
  font-size: 14px;
  color: var(--fg-muted);
  line-height: 1.6;
}

.timeline-content .meta {
  font-size: 13px;
  color: var(--fg-faint);
}

.role {
  font-weight: 400;
  color: var(--fg-muted);
}

.role::before {
  content: "/ ";
  color: var(--fg-faint);
}

/* ---------- Publications ---------- */
.pub-filters {
  display: flex;
  gap: 8px;
  margin-bottom: 28px;
  flex-wrap: wrap;
}

.filter-btn {
  padding: 5px 14px;
  font-size: 13px;
  font-family: var(--font-sans);
  border: 1px solid var(--border);
  border-radius: 20px;
  background: transparent;
  color: var(--fg-muted);
  cursor: pointer;
  transition: all var(--transition);
}

.filter-btn:hover {
  border-color: var(--fg-muted);
  color: var(--fg);
}

.filter-btn.active {
  background: var(--accent);
  color: var(--bg);
  border-color: var(--accent);
}

.pub-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 20px;
}

.pub-item {
  padding: 18px 20px;
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  transition: all var(--transition);
}

.pub-item:hover {
  box-shadow: var(--card-shadow);
}

.pub-item[data-featured] {
  background: var(--card-featured-bg);
  border-color: var(--card-featured-border);
}

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

.pub-tag {
  display: inline-block;
  font-size: 11px;
  font-weight: 600;
  padding: 2px 8px;
  border-radius: 3px;
  background: var(--tag-bg);
  color: var(--tag-fg);
  margin-bottom: 8px;
  letter-spacing: 0.02em;
  text-transform: uppercase;
}

.tag-preprint {
  background: var(--tag-preprint-bg);
  color: var(--tag-preprint-fg);
}

.pub-featured-badge {
  display: inline-block;
  font-size: 10px;
  font-weight: 700;
  padding: 2px 7px;
  border-radius: 3px;
  background: var(--featured-bg);
  color: var(--featured-fg);
  margin-left: 6px;
  margin-bottom: 8px;
  letter-spacing: 0.04em;
  text-transform: uppercase;
}

.pub-title {
  font-size: 15px;
  font-weight: 600;
  line-height: 1.45;
  margin-bottom: 4px;
}

.pub-authors {
  font-size: 13px;
  color: var(--fg-muted);
  line-height: 1.5;
  margin-bottom: 4px;
}

.pub-authors strong {
  color: var(--fg);
  font-weight: 600;
}

.pub-note {
  font-size: 12px;
  color: var(--fg-faint);
  font-style: italic;
  margin-bottom: 4px;
}

.pub-links {
  display: flex;
  gap: 12px;
  margin-top: 8px;
}

.pub-links a {
  font-size: 12px;
  font-family: var(--font-mono);
  color: var(--fg-muted);
  padding: 2px 0;
  border-bottom: 1px dashed var(--border);
  transition: all var(--transition);
}

.pub-links a:hover {
  color: var(--fg);
  border-color: var(--fg);
}

/* ---------- Teaching ---------- */
.teaching-grid {
  display: flex;
  flex-direction: column;
  gap: 16px;
}

.teaching-item {
  display: flex;
  gap: 16px;
  align-items: baseline;
}

.teaching-role {
  font-size: 11px;
  font-weight: 600;
  padding: 3px 10px;
  border-radius: 3px;
  background: var(--tag-bg);
  color: var(--tag-fg);
  white-space: nowrap;
  text-transform: uppercase;
  letter-spacing: 0.03em;
  flex-shrink: 0;
}

.teaching-item h3 {
  font-size: 14px;
  font-weight: 600;
  margin-bottom: 1px;
}

.teaching-item p {
  font-size: 13px;
  color: var(--fg-muted);
}

/* ---------- Awards ---------- */
.awards-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 14px;
}

.awards-list li {
  font-size: 14px;
  line-height: 1.55;
  padding-left: 16px;
  position: relative;
}

.awards-list li::before {
  content: "";
  position: absolute;
  left: 0;
  top: 9px;
  width: 5px;
  height: 5px;
  border-radius: 50%;
  background: var(--fg-faint);
}

.award-source {
  display: block;
  font-size: 12px;
  color: var(--fg-faint);
}

/* ---------- Service ---------- */
.service-grid {
  display: flex;
  flex-direction: column;
  gap: 20px;
}

.service-item h3 {
  font-size: 14px;
  font-weight: 600;
  margin-bottom: 2px;
}

.service-item p {
  font-size: 13px;
  color: var(--fg-muted);
}

/* ---------- Footer ---------- */
footer {
  padding: 40px 0;
  text-align: center;
}

footer .container {
  padding-top: 32px;
  border-top: 1px solid var(--border);
}

footer p {
  font-size: 12px;
  color: var(--fg-faint);
}

/* ---------- Responsive ---------- */
@media (max-width: 640px) {
  .hero-card {
    flex-direction: column;
    gap: 20px;
    align-items: flex-start;
  }

  .hero-photo {
    width: 120px;
  }

  .tagline {
    font-size: 15px;
  }

  .nav-links {
    display: none;
  }

  .timeline-item {
    grid-template-columns: 1fr;
    gap: 4px;
  }

  .timeline-date {
    font-size: 12px;
  }

  .teaching-item {
    flex-direction: column;
    gap: 4px;
  }

  .pub-item {
    padding: 14px 16px;
  }
}

/* ---------- Animations ---------- */
@media (prefers-reduced-motion: no-preference) {
  .section {
    animation: fadeUp 0.5s ease both;
  }

  @keyframes fadeUp {
    from {
      opacity: 0;
      transform: translateY(12px);
    }
    to {
      opacity: 1;
      transform: translateY(0);
    }
  }
}