/* ===== CSS Variables ===== */
:root {
  --color-primary: #1a56db;
  --color-primary-dark: #1544b0;
  --color-primary-light: #e8effd;
  --color-ccf-a: #dc2626;
  --color-ccf-a-bg: #fef2f2;
  --color-ccf-b: #2563eb;
  --color-ccf-b-bg: #eff6ff;
  --color-ccf-c: #6b7280;
  --color-ccf-c-bg: #f3f4f6;
  --color-bg: #f8fafc;
  --color-card: #ffffff;
  --color-text: #1e293b;
  --color-text-secondary: #64748b;
  --color-border: #e2e8f0;
  --color-link: #1a56db;
  --radius: 12px;
  --radius-sm: 8px;
  --shadow-sm: 0 1px 3px rgba(0,0,0,0.08);
  --shadow-md: 0 4px 12px rgba(0,0,0,0.1);
  --shadow-lg: 0 10px 25px rgba(0,0,0,0.12);
  --font-sans: "Inter", "Noto Sans SC", -apple-system, "Helvetica Neue", "Microsoft YaHei", sans-serif;
  --container-width: 1100px;
  --transition: 0.3s ease;
}

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

html {
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
}

body {
  font-family: var(--font-sans);
  color: var(--color-text);
  background: var(--color-bg);
  line-height: 1.7;
  font-size: 16px;
}

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

a:hover {
  color: var(--color-primary-dark);
}

img {
  max-width: 100%;
  height: auto;
}

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

/* ===== Header ===== */
.site-header {
  background: var(--color-card);
  border-bottom: 1px solid var(--color-border);
  position: sticky;
  top: 0;
  z-index: 100;
  backdrop-filter: blur(8px);
  background: rgba(255,255,255,0.95);
}

.site-header .container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 64px;
}

.site-logo {
  font-size: 18px;
  font-weight: 700;
  color: var(--color-text);
  white-space: nowrap;
}

.site-logo:hover {
  color: var(--color-primary);
}

.logo-divider {
  color: var(--color-border);
  margin: 0 6px;
  font-weight: 300;
}

.logo-sub {
  font-weight: 400;
  font-size: 14px;
  color: var(--color-text-secondary);
}

.site-nav {
  display: flex;
  gap: 28px;
}

.site-nav a {
  font-size: 15px;
  font-weight: 500;
  color: var(--color-text-secondary);
  padding: 4px 0;
  border-bottom: 2px solid transparent;
  transition: all var(--transition);
}

.site-nav a:hover {
  color: var(--color-primary);
  border-bottom-color: var(--color-primary);
}

/* Mobile nav toggle */
.nav-toggle-input {
  display: none;
}

.nav-toggle-label {
  display: none;
  cursor: pointer;
  width: 28px;
  height: 20px;
  flex-direction: column;
  justify-content: space-between;
}

.nav-toggle-label span {
  display: block;
  height: 2px;
  background: var(--color-text);
  border-radius: 2px;
  transition: all var(--transition);
}

/* ===== Hero Section ===== */
.hero {
  padding: 60px 0 48px;
}

.hero-content {
  display: flex;
  gap: 40px;
  align-items: flex-start;
}

.hero-avatar {
  width: 160px;
  height: 160px;
  border-radius: 50%;
  object-fit: cover;
  border: 4px solid var(--color-card);
  box-shadow: var(--shadow-md);
  flex-shrink: 0;
}

.hero-info {
  flex: 1;
}

.hero-name {
  font-size: 32px;
  font-weight: 700;
  margin-bottom: 4px;
  color: var(--color-text);
}

.hero-name-en {
  font-size: 18px;
  font-weight: 400;
  color: var(--color-text-secondary);
  margin-left: 12px;
}

.hero-title {
  font-size: 16px;
  color: var(--color-text-secondary);
  margin-bottom: 16px;
}

.hero-desc {
  font-size: 15px;
  line-height: 1.8;
  color: var(--color-text);
  margin-bottom: 20px;
}

.hero-links {
  display: flex;
  gap: 12px;
  flex-wrap: wrap;
}

.hero-link {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 8px 16px;
  background: var(--color-primary-light);
  color: var(--color-primary);
  border-radius: var(--radius-sm);
  font-size: 14px;
  font-weight: 500;
  transition: all var(--transition);
}

.hero-link:hover {
  background: var(--color-primary);
  color: #fff;
}

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

.section-title {
  font-size: 24px;
  font-weight: 700;
  margin-bottom: 8px;
  color: var(--color-text);
  display: flex;
  align-items: center;
  gap: 10px;
}

.section-title::before {
  content: "";
  display: inline-block;
  width: 4px;
  height: 24px;
  background: var(--color-primary);
  border-radius: 2px;
}

.section-subtitle {
  font-size: 15px;
  color: var(--color-text-secondary);
  margin-bottom: 28px;
}

/* ===== About / Team Section ===== */
.about-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 20px;
}

.about-card {
  background: var(--color-card);
  border-radius: var(--radius);
  padding: 24px;
  box-shadow: var(--shadow-sm);
  border: 1px solid var(--color-border);
}

.about-card h3 {
  font-size: 16px;
  font-weight: 600;
  margin-bottom: 12px;
  color: var(--color-primary);
}

.about-card p,
.about-card li {
  font-size: 14px;
  color: var(--color-text-secondary);
  line-height: 1.8;
}

.about-card ul {
  list-style: none;
  padding: 0;
}

.about-card li::before {
  content: ">";
  color: var(--color-primary);
  font-weight: 600;
  margin-right: 8px;
}

/* ===== Research Direction Cards ===== */
.research-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 20px;
}

.research-card {
  background: var(--color-card);
  border-radius: var(--radius);
  padding: 28px;
  box-shadow: var(--shadow-sm);
  border: 1px solid var(--color-border);
  transition: all var(--transition);
}

.research-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
}

.research-card h3 {
  font-size: 18px;
  font-weight: 600;
  margin-bottom: 12px;
  color: var(--color-text);
}

.research-card p {
  font-size: 14px;
  color: var(--color-text-secondary);
  line-height: 1.8;
}

.research-tag {
  display: inline-block;
  padding: 3px 10px;
  background: var(--color-primary-light);
  color: var(--color-primary);
  border-radius: 20px;
  font-size: 12px;
  font-weight: 500;
  margin: 4px 4px 4px 0;
}

/* ===== Research Task Cards with GIF ===== */
.research-category-title {
  font-size: 20px;
  font-weight: 600;
  margin: 36px 0 12px;
  color: var(--color-text);
}

.research-category-title:first-of-type {
  margin-top: 0;
}

.research-category-desc {
  font-size: 15px;
  color: var(--color-text-secondary);
  margin-bottom: 20px;
  line-height: 1.7;
}

.research-task-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
  gap: 20px;
  margin-bottom: 40px;
}

.research-task-card {
  background: var(--color-card);
  border-radius: var(--radius);
  overflow: hidden;
  box-shadow: var(--shadow-sm);
  border: 1px solid var(--color-border);
  transition: all var(--transition);
  display: flex;
  flex-direction: column;
}

.research-task-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
  border-color: var(--color-primary);
}

.task-gif {
  width: 100%;
  height: 180px;
  overflow: hidden;
  background: #f1f5f9;
  display: flex;
  align-items: center;
  justify-content: center;
}

.task-gif img {
  width: 100%;
  height: 100%;
  object-fit: cover;
  transition: transform var(--transition);
}

.research-task-card:hover .task-gif img {
  transform: scale(1.05);
}

.task-info {
  padding: 20px;
  flex: 1;
  display: flex;
  flex-direction: column;
}

.task-info h4 {
  font-size: 16px;
  font-weight: 600;
  margin-bottom: 8px;
  color: var(--color-text);
}

.task-info p {
  font-size: 14px;
  color: var(--color-text-secondary);
  line-height: 1.7;
  flex: 1;
}

/* ===== Paper Section ===== */
.paper-category-title {
  font-size: 20px;
  font-weight: 600;
  margin: 36px 0 20px;
  padding-bottom: 10px;
  border-bottom: 2px solid var(--color-border);
  color: var(--color-text);
}

.paper-category-title:first-of-type {
  margin-top: 0;
}

.paper-list {
  display: grid;
  grid-template-columns: 1fr;
  gap: 16px;
}

.paper-card {
  background: var(--color-card);
  border-radius: var(--radius);
  padding: 22px 24px;
  box-shadow: var(--shadow-sm);
  border: 1px solid var(--color-border);
  transition: all var(--transition);
  display: block;
  color: inherit;
}

.paper-card:hover {
  transform: translateY(-3px);
  box-shadow: var(--shadow-md);
  color: inherit;
  border-color: var(--color-primary);
}

.paper-meta {
  display: flex;
  align-items: center;
  gap: 8px;
  margin-bottom: 8px;
  flex-wrap: wrap;
}

.badge {
  display: inline-block;
  padding: 2px 10px;
  border-radius: 20px;
  font-size: 12px;
  font-weight: 600;
  letter-spacing: 0.02em;
}

.badge-A {
  background: var(--color-ccf-a-bg);
  color: var(--color-ccf-a);
}

.badge-B {
  background: var(--color-ccf-b-bg);
  color: var(--color-ccf-b);
}

.badge-C {
  background: var(--color-ccf-c-bg);
  color: var(--color-ccf-c);
}

.badge-venue {
  background: var(--color-primary-light);
  color: var(--color-primary);
}

.paper-year {
  font-size: 13px;
  color: var(--color-text-secondary);
  font-weight: 500;
}

.paper-title {
  font-size: 16px;
  font-weight: 600;
  line-height: 1.5;
  margin-bottom: 6px;
  color: var(--color-text);
}

.paper-authors {
  font-size: 14px;
  color: var(--color-text-secondary);
  line-height: 1.6;
  margin-bottom: 10px;
}

.paper-links {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
}

.btn {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  padding: 5px 14px;
  border-radius: var(--radius-sm);
  font-size: 13px;
  font-weight: 500;
  transition: all var(--transition);
  border: none;
  cursor: pointer;
}

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

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

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

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

/* ===== Paper Detail Page ===== */
.paper-detail {
  padding: 48px 0 64px;
}

.breadcrumb {
  font-size: 14px;
  color: var(--color-text-secondary);
  margin-bottom: 24px;
}

.breadcrumb a {
  color: var(--color-text-secondary);
}

.breadcrumb a:hover {
  color: var(--color-primary);
}

.breadcrumb-sep {
  margin: 0 8px;
  color: var(--color-border);
}

.paper-detail-card {
  background: var(--color-card);
  border-radius: var(--radius);
  padding: 36px 40px;
  box-shadow: var(--shadow-sm);
  border: 1px solid var(--color-border);
}

.paper-detail-title {
  font-size: 24px;
  font-weight: 700;
  line-height: 1.4;
  margin-bottom: 16px;
  color: var(--color-text);
}

.paper-detail-meta {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 12px;
  flex-wrap: wrap;
}

.paper-detail-authors {
  font-size: 15px;
  color: var(--color-text-secondary);
  margin-bottom: 20px;
  line-height: 1.6;
}

.paper-detail-links {
  display: flex;
  gap: 10px;
  margin-bottom: 32px;
  flex-wrap: wrap;
}

.paper-detail-links .btn {
  padding: 8px 20px;
  font-size: 14px;
}

.paper-detail-body h2 {
  font-size: 18px;
  font-weight: 600;
  margin: 28px 0 12px;
  padding-bottom: 8px;
  border-bottom: 1px solid var(--color-border);
  color: var(--color-text);
}

.paper-detail-body h2:first-child {
  margin-top: 0;
}

.paper-detail-body p {
  font-size: 15px;
  line-height: 1.8;
  color: var(--color-text-secondary);
  margin-bottom: 16px;
}

.paper-detail-body ul,
.paper-detail-body ol {
  padding-left: 20px;
  margin-bottom: 16px;
}

.paper-detail-body li {
  font-size: 15px;
  line-height: 1.8;
  color: var(--color-text-secondary);
  margin-bottom: 6px;
}

.back-link {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  margin-top: 32px;
  font-size: 14px;
  font-weight: 500;
  color: var(--color-primary);
}

.back-link:hover {
  color: var(--color-primary-dark);
}

/* ===== Footer ===== */
.site-footer {
  background: var(--color-card);
  border-top: 1px solid var(--color-border);
  padding: 24px 0;
  text-align: center;
}

.site-footer p {
  font-size: 13px;
  color: var(--color-text-secondary);
  line-height: 1.8;
}

.site-footer a {
  color: var(--color-primary);
}

/* ===== Back to top ===== */
.back-to-top {
  position: fixed;
  bottom: 32px;
  right: 32px;
  width: 40px;
  height: 40px;
  border-radius: 50%;
  background: var(--color-primary);
  color: #fff;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 18px;
  box-shadow: var(--shadow-md);
  opacity: 0;
  visibility: hidden;
  transition: all var(--transition);
  text-decoration: none;
}

.back-to-top:hover {
  background: var(--color-primary-dark);
  color: #fff;
}

.back-to-top.visible {
  opacity: 1;
  visibility: visible;
}

/* ===== Responsive ===== */
@media (max-width: 768px) {
  .nav-toggle-label {
    display: flex;
  }

  .site-nav {
    display: none;
    position: absolute;
    top: 64px;
    left: 0;
    right: 0;
    background: var(--color-card);
    flex-direction: column;
    padding: 16px 24px;
    border-bottom: 1px solid var(--color-border);
    box-shadow: var(--shadow-md);
    gap: 0;
  }

  .site-nav a {
    padding: 12px 0;
    border-bottom: 1px solid var(--color-border);
  }

  .site-nav a:last-child {
    border-bottom: none;
  }

  .nav-toggle-input:checked ~ .site-nav {
    display: flex;
  }

  .hero-content {
    flex-direction: column;
    align-items: center;
    text-align: center;
  }

  .hero-avatar {
    width: 120px;
    height: 120px;
  }

  .hero-links {
    justify-content: center;
  }

  .hero-name {
    font-size: 26px;
  }

  .about-grid,
  .research-grid {
    grid-template-columns: 1fr;
  }

  .logo-sub {
    display: none;
  }

  .logo-divider {
    display: none;
  }

  .paper-detail-card {
    padding: 24px 20px;
  }

  .paper-detail-title {
    font-size: 20px;
  }
}

@media (max-width: 480px) {
  .hero {
    padding: 40px 0 32px;
  }

  .section {
    padding: 32px 0;
  }

  .container {
    padding: 0 16px;
  }
}