/* ============================================
   Cai Qing Personal Academic Website
   Design: Minimalist, Bilingual, Academic
   Palette: Black / White / Low-saturation Grey
   Typography: Inter (EN) + Noto Sans SC (ZH)
   ============================================ */

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

:root {
  --color-bg: #fafaf9;
  --color-surface: #ffffff;
  --color-text: #2c2c2c;
  --color-text-secondary: #5c5c5c;
  --color-text-muted: #8a8a8a;
  --color-border: #e5e5e0;
  --color-accent: #1a1a1a;
  --color-link: #2c2c2c;
  --color-link-hover: #000000;
  --font-en: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif;
  --font-zh: 'Noto Sans SC', '思源黑体', 'Source Han Sans SC', 'PingFang SC', 'Microsoft YaHei', sans-serif;
  --font-mono: 'SF Mono', 'Fira Code', 'Consolas', monospace;
  --max-width: 1200px;
  --header-height: 64px;
  --spacing-xs: 8px;
  --spacing-sm: 16px;
  --spacing-md: 24px;
  --spacing-lg: 40px;
  --spacing-xl: 64px;
  --spacing-2xl: 96px;
  --transition: 0.2s ease;
}

html {
  font-size: 16px;
  scroll-behavior: smooth;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body {
  font-family: var(--font-en);
  color: var(--color-text);
  background-color: var(--color-bg);
  line-height: 1.6;
  letter-spacing: 0.01em;
  min-height: 100vh;
}

/* --- Typography --- */
h1, h2, h3, h4, h5, h6 {
  font-weight: 400;
  line-height: 1.3;
  color: var(--color-text);
}

h1 { font-size: 2.25rem; letter-spacing: -0.02em; }
h2 { font-size: 1.75rem; letter-spacing: -0.01em; }
h3 { font-size: 1.25rem; }
h4 { font-size: 1.1rem; font-weight: 500; }

p {
  margin-bottom: 1rem;
  color: var(--color-text-secondary);
}

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

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

.lang-zh {
  font-family: var(--font-zh);
}

/* --- Layout --- */
.container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--spacing-md);
}

.section {
  padding: var(--spacing-xl) 0;
}

.section-title {
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  color: var(--color-text-muted);
  margin-bottom: var(--spacing-lg);
  font-weight: 500;
}

.section-divider {
  border: none;
  border-top: 1px solid var(--color-border);
  margin: var(--spacing-xl) 0;
}

/* --- Header / Navigation --- */
.header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: var(--header-height);
  background: rgba(250, 250, 249, 0.92);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--color-border);
  z-index: 100;
  display: flex;
  align-items: center;
}

.header-inner {
  max-width: var(--max-width);
  width: 100%;
  margin: 0 auto;
  padding: 0 var(--spacing-md);
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.header-logo {
  font-size: 1rem;
  font-weight: 500;
  letter-spacing: 0.02em;
  color: var(--color-text);
}

.header-logo a {
  color: var(--color-text);
  text-decoration: none;
}

.header-nav {
  display: flex;
  align-items: center;
  gap: var(--spacing-md);
}

.header-nav a {
  font-size: 0.8125rem;
  color: var(--color-text-secondary);
  text-decoration: none;
  padding: 4px 0;
  border-bottom: 1px solid transparent;
  transition: all var(--transition);
  letter-spacing: 0.03em;
}

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

.lang-switch {
  font-size: 0.75rem;
  color: var(--color-text-muted);
  cursor: pointer;
  padding: 4px 10px;
  border: 1px solid var(--color-border);
  background: transparent;
  border-radius: 2px;
  transition: all var(--transition);
  letter-spacing: 0.03em;
  font-family: var(--font-en);
}

.lang-switch:hover {
  color: var(--color-text);
  border-color: var(--color-text);
}

/* Mobile menu button */
.mobile-menu-btn {
  display: none;
  background: none;
  border: none;
  cursor: pointer;
  padding: 4px;
  color: var(--color-text);
}

.mobile-menu-btn span {
  display: block;
  width: 20px;
  height: 1.5px;
  background: var(--color-text);
  margin: 5px 0;
  transition: all var(--transition);
}

/* --- Footer --- */
.footer {
  border-top: 1px solid var(--color-border);
  padding: var(--spacing-lg) 0;
  text-align: center;
}

.footer-text {
  font-size: 0.75rem;
  color: var(--color-text-muted);
  letter-spacing: 0.03em;
}

/* --- Hero Section (Home) --- */
.hero {
  padding-top: calc(var(--header-height) + var(--spacing-2xl));
  padding-bottom: var(--spacing-2xl);
}

.hero-grid {
  display: grid;
  grid-template-columns: 320px 1fr;
  gap: var(--spacing-xl);
  align-items: start;
}

.hero-portrait {
  width: 100%;
  aspect-ratio: 3/4;
  object-fit: cover;
  background: var(--color-border);
  filter: grayscale(15%);
}

.hero-content h1 {
  font-size: 2.5rem;
  font-weight: 400;
  letter-spacing: -0.02em;
  margin-bottom: var(--spacing-xs);
}

.hero-subtitle {
  font-size: 0.9rem;
  color: var(--color-text-muted);
  letter-spacing: 0.05em;
  margin-bottom: var(--spacing-md);
  line-height: 1.7;
}

.hero-bio {
  font-size: 1rem;
  color: var(--color-text-secondary);
  line-height: 1.75;
  max-width: 640px;
  margin-bottom: var(--spacing-lg);
}

.hero-bio .lang-zh {
  display: block;
  margin-top: var(--spacing-sm);
  color: var(--color-text-muted);
}

.hero-intro {
  font-size: 1.05rem;
  color: var(--color-text);
  font-weight: 500;
  border-left: 2px solid var(--color-accent);
  padding-left: var(--spacing-md);
}

.hero-intro .lang-zh {
  color: var(--color-text);
}

/* --- Hero Tags --- */
.hero-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-bottom: var(--spacing-lg);
}

.hero-tag {
  display: inline-block;
  font-size: 0.75rem;
  padding: 4px 14px;
  border: 1px solid var(--color-border);
  border-radius: 2px;
  color: var(--color-text-secondary);
  letter-spacing: 0.03em;
  transition: all var(--transition);
}

.hero-tag .lang-zh {
  font-size: 0.75rem;
  color: var(--color-text-secondary);
}

/* --- Highlights --- */
.highlights {
  padding: var(--spacing-xl) 0;
  border-top: 1px solid var(--color-border);
}

.highlights-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--spacing-lg);
}

.highlight-item {
  display: flex;
  align-items: flex-start;
  gap: var(--spacing-sm);
  padding: var(--spacing-md) 0;
}

.highlight-item.highlight-event {
  background: var(--color-surface);
  padding: var(--spacing-md);
  border: 1px solid var(--color-border);
  border-radius: 2px;
  transition: border-color var(--transition);
}

.highlight-item.highlight-event:hover {
  border-color: var(--color-text-muted);
}

.highlight-icon {
  font-size: 1.25rem;
  flex-shrink: 0;
  width: 32px;
  height: 32px;
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--color-text-muted);
}

.highlight-text {
  font-size: 0.875rem;
  color: var(--color-text-secondary);
  line-height: 1.6;
}

.highlight-text .lang-zh {
  display: block;
  font-size: 0.8125rem;
  color: var(--color-text-muted);
  margin-top: 2px;
}

.highlight-event-title {
  font-size: 0.9375rem;
  font-weight: 500;
  color: var(--color-text);
  margin-bottom: 4px;
}

.highlight-event-location {
  font-size: 0.8125rem;
  color: var(--color-text-muted);
  margin-bottom: 0;
  line-height: 1.5;
}

/* --- Page Header --- */
.page-header {
  padding-top: calc(var(--header-height) + var(--spacing-xl));
  padding-bottom: var(--spacing-lg);
  border-bottom: 1px solid var(--color-border);
}

.page-header h1 {
  font-size: 1.75rem;
  font-weight: 400;
  letter-spacing: -0.01em;
}

.page-header p {
  font-size: 0.875rem;
  color: var(--color-text-muted);
  margin-top: var(--spacing-xs);
}

/* --- Content Blocks --- */
.content-block {
  padding: var(--spacing-lg) 0;
}

.content-block + .content-block {
  border-top: 1px solid var(--color-border);
}

.content-block h3 {
  font-size: 0.8125rem;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--color-text-muted);
  margin-bottom: var(--spacing-md);
  font-weight: 500;
}

/* --- Timeline / List Items --- */
.timeline-item {
  display: grid;
  grid-template-columns: 180px 1fr;
  gap: var(--spacing-md);
  padding: var(--spacing-sm) 0;
}

.timeline-date {
  font-size: 0.8125rem;
  color: var(--color-text-muted);
  font-family: var(--font-mono);
  letter-spacing: 0.02em;
}

.timeline-content h4 {
  font-size: 0.9375rem;
  font-weight: 500;
  margin-bottom: 4px;
  color: var(--color-text);
}

.timeline-content p {
  font-size: 0.8125rem;
  margin-bottom: 0;
}

.timeline-content .lang-zh {
  display: block;
  color: var(--color-text-muted);
  font-size: 0.8125rem;
  margin-top: 2px;
}

/* --- Project Grid --- */
.project-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: var(--spacing-lg);
}

.project-card {
  cursor: pointer;
}

.project-card img {
  width: 100%;
  aspect-ratio: 4/3;
  object-fit: cover;
  background: var(--color-border);
  filter: grayscale(10%);
  transition: filter var(--transition);
}

.project-card:hover img {
  filter: grayscale(0%);
}

.project-card h4 {
  margin-top: var(--spacing-sm);
  font-size: 0.9375rem;
  font-weight: 500;
}

.project-card p {
  font-size: 0.8125rem;
  margin-top: 4px;
}

.project-card .lang-zh {
  display: block;
  color: var(--color-text-muted);
  font-size: 0.8125rem;
}

/* --- Publication Card --- */
.pub-card {
  display: grid;
  grid-template-columns: 120px 1fr;
  gap: var(--spacing-md);
  padding: var(--spacing-sm) 0;
}

.pub-card img {
  width: 120px;
  aspect-ratio: 3/4;
  object-fit: cover;
  background: var(--color-border);
}

.pub-card h4 {
  font-size: 0.9375rem;
  font-weight: 500;
  margin-bottom: 4px;
}

.pub-card .pub-meta {
  font-size: 0.75rem;
  color: var(--color-text-muted);
  font-family: var(--font-mono);
  margin-bottom: 4px;
}

.pub-card p {
  font-size: 0.8125rem;
}

/* --- News Card --- */
.news-list {
  list-style: none;
}

.news-item {
  display: grid;
  grid-template-columns: 140px 1fr;
  gap: var(--spacing-md);
  padding: var(--spacing-sm) 0;
  border-bottom: 1px solid var(--color-border);
}

.news-item:first-child {
  border-top: 1px solid var(--color-border);
}

.news-date {
  font-size: 0.8125rem;
  color: var(--color-text-muted);
  font-family: var(--font-mono);
}

.news-item h4 {
  font-size: 0.9375rem;
  font-weight: 500;
  margin-bottom: 4px;
}

.news-item p {
  font-size: 0.8125rem;
}

.news-featured {
  background: var(--color-surface);
  padding: var(--spacing-md);
  border-left: 2px solid var(--color-accent);
  margin-bottom: var(--spacing-lg);
}

.news-featured .news-label {
  font-size: 0.6875rem;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--color-text-muted);
  margin-bottom: var(--spacing-xs);
}

/* --- Work Entry (Practice Page) --- */
.work-entry {
  padding: var(--spacing-sm) 0;
}

.work-gallery {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--spacing-xs);
  margin-bottom: var(--spacing-sm);
}

.work-gallery img {
  width: 100%;
  aspect-ratio: 4/3;
  object-fit: cover;
  background: var(--color-border);
  filter: grayscale(10%);
}

.work-info h4 {
  font-size: 1rem;
  font-weight: 500;
  margin-bottom: 4px;
}

.work-meta {
  font-size: 0.75rem;
  color: var(--color-text-muted);
  font-family: var(--font-mono);
  margin-bottom: var(--spacing-xs);
}

/* --- Collapsible Button --- */
.collapsible-btn {
  display: block;
  width: 100%;
  text-align: left;
  padding: var(--spacing-sm) 0;
  font-size: 0.8125rem;
  color: var(--color-text-muted);
  background: none;
  border: none;
  border-top: 1px solid var(--color-border);
  cursor: pointer;
  letter-spacing: 0.03em;
  transition: color var(--transition);
  font-family: var(--font-en);
}

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

.hidden {
  display: none;
}

/* --- Data Highlight --- */
.data-highlight {
  display: inline-flex;
  align-items: baseline;
  gap: 4px;
  font-family: var(--font-mono);
}

.data-number {
  font-size: 1.5rem;
  font-weight: 500;
  color: var(--color-text);
  letter-spacing: -0.02em;
}

.data-label {
  font-size: 0.75rem;
  color: var(--color-text-muted);
}

/* --- Responsive --- */
@media (max-width: 1024px) {
  .hero-grid {
    grid-template-columns: 240px 1fr;
    gap: var(--spacing-lg);
  }
  
  .project-grid {
    grid-template-columns: 1fr;
  }
  
  .timeline-item {
    grid-template-columns: 120px 1fr;
  }
}

@media (max-width: 768px) {
  :root {
    --header-height: 56px;
  }
  
  h1 { font-size: 1.75rem; }
  h2 { font-size: 1.375rem; }
  
  .hero-grid {
    grid-template-columns: 1fr;
  }
  
  .hero-portrait {
    max-width: 240px;
    aspect-ratio: 1/1;
  }
  
  .hero-content h1 {
    font-size: 1.75rem;
  }
  
  .highlights-grid {
    grid-template-columns: 1fr;
  }
  
  .header-nav {
    display: none;
    position: absolute;
    top: var(--header-height);
    left: 0;
    right: 0;
    background: var(--color-bg);
    flex-direction: column;
    padding: var(--spacing-md);
    border-bottom: 1px solid var(--color-border);
    gap: var(--spacing-sm);
  }
  
  .header-nav.open {
    display: flex;
  }
  
  .mobile-menu-btn {
    display: block;
  }
  
  .timeline-item {
    grid-template-columns: 1fr;
    gap: 4px;
  }
  
  .pub-card {
    grid-template-columns: 80px 1fr;
    gap: var(--spacing-sm);
  }
  
  .pub-card img {
    width: 80px;
  }
  
  .news-item {
    grid-template-columns: 1fr;
    gap: 4px;
  }
  
  .page-header h1 {
    font-size: 1.5rem;
  }

  .work-gallery {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 480px) {
  .container {
    padding: 0 var(--spacing-sm);
  }
  
  .section {
    padding: var(--spacing-lg) 0;
  }
  
  .hero {
    padding-top: calc(var(--header-height) + var(--spacing-lg));
    padding-bottom: var(--spacing-lg);
  }
}