/* ============================================
   可信联邦学习 - 配套资源网站样式
   Modern Academic Style
   ============================================ */

/* --- CSS Variables --- */
:root {
  /* Colors */
  --color-primary: #2563EB;
  --color-primary-dark: #1D4ED8;
  --color-primary-light: #DBEAFE;
  --color-primary-lighter: #EFF6FF;
  --color-bg: #FFFFFF;
  --color-surface: #F8FAFC;
  --color-card: #FFFFFF;
  --color-text: #1E293B;
  --color-text-secondary: #64748B;
  --color-text-muted: #94A3B8;
  --color-border: #E2E8F0;
  --color-border-light: #F1F5F9;
  --color-success: #16A34A;
  --color-success-bg: #F0FDF4;
  --color-warning: #F59E0B;
  --color-warning-bg: #FFFBEB;
  --color-danger: #DC2626;
  --color-shadow: rgba(0, 0, 0, 0.06);
  --color-shadow-lg: rgba(0, 0, 0, 0.1);
  --color-overlay: rgba(0, 0, 0, 0.7);

  /* Typography */
  --font-family: "Noto Sans SC", "PingFang SC", "Microsoft YaHei", system-ui, -apple-system, sans-serif;
  --font-mono: "Fira Code", "Consolas", "Monaco", monospace;
  --font-size-xs: 0.75rem;
  --font-size-sm: 0.875rem;
  --font-size-base: 1rem;
  --font-size-lg: 1.125rem;
  --font-size-xl: 1.25rem;
  --font-size-2xl: 1.5rem;
  --font-size-3xl: 2rem;
  --font-size-4xl: 2.5rem;
  --line-height: 1.75;

  /* Spacing */
  --space-xs: 0.25rem;
  --space-sm: 0.5rem;
  --space-md: 1rem;
  --space-lg: 1.5rem;
  --space-xl: 2rem;
  --space-2xl: 3rem;
  --space-3xl: 4rem;

  /* Borders */
  --radius-sm: 4px;
  --radius-md: 8px;
  --radius-lg: 12px;
  --radius-xl: 16px;

  /* Layout */
  --max-width: 1200px;
  --nav-height: 64px;

  /* Transitions */
  --transition: 0.2s ease;
  --transition-slow: 0.3s ease;
}

/* --- Dark Mode Variables --- */
[data-theme="dark"] {
  --color-bg: #0F172A;
  --color-surface: #1E293B;
  --color-card: #1E293B;
  --color-text: #F1F5F9;
  --color-text-secondary: #94A3B8;
  --color-text-muted: #64748B;
  --color-border: #334155;
  --color-border-light: #1E293B;
  --color-primary-light: #1E3A5F;
  --color-primary-lighter: #172554;
  --color-success-bg: #052E16;
  --color-warning-bg: #451A03;
  --color-shadow: rgba(0, 0, 0, 0.3);
  --color-shadow-lg: rgba(0, 0, 0, 0.5);
  --color-overlay: rgba(0, 0, 0, 0.85);
}

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

html {
  scroll-behavior: smooth;
  scroll-padding-top: calc(var(--nav-height) + 1rem);
}

body {
  font-family: var(--font-family);
  font-size: var(--font-size-base);
  line-height: var(--line-height);
  color: var(--color-text);
  background-color: var(--color-bg);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

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

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

a:focus-visible {
  outline: 2px solid var(--color-primary);
  outline-offset: 2px;
  border-radius: var(--radius-sm);
}

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

h1, h2, h3, h4, h5, h6 {
  line-height: 1.3;
  color: var(--color-text);
}

h1 { font-size: var(--font-size-3xl); font-weight: 700; }
h2 { font-size: var(--font-size-2xl); font-weight: 600; }
h3 { font-size: var(--font-size-xl); font-weight: 600; }

/* --- Utility Classes --- */
.container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--space-lg);
}

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border-width: 0;
}

.section {
  padding: var(--space-3xl) 0;
}

.section-title {
  font-size: var(--font-size-2xl);
  font-weight: 600;
  margin-bottom: var(--space-xl);
  padding-bottom: var(--space-sm);
  border-bottom: 2px solid var(--color-primary);
  display: inline-block;
}

.text-center { text-align: center; }
.text-secondary { color: var(--color-text-secondary); }
.text-muted { color: var(--color-text-muted); }
.text-sm { font-size: var(--font-size-sm); }

/* --- Navigation --- */
.navbar {
  position: sticky;
  top: 0;
  z-index: 1000;
  background-color: var(--color-bg);
  border-bottom: 1px solid var(--color-border);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  height: var(--nav-height);
}

[data-theme="dark"] .navbar {
  background-color: rgba(15, 23, 42, 0.9);
}

.navbar .container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 100%;
}

.nav-brand {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  font-weight: 700;
  font-size: var(--font-size-lg);
  color: var(--color-text);
  text-decoration: none;
  white-space: nowrap;
}

.nav-brand:hover {
  color: var(--color-primary);
  text-decoration: none;
}

.nav-brand-icon {
  width: 28px;
  height: 28px;
  background: var(--color-primary);
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  color: white;
  font-size: var(--font-size-sm);
  font-weight: 700;
  flex-shrink: 0;
}

.nav-links {
  display: flex;
  align-items: center;
  gap: var(--space-xs);
  list-style: none;
}

.nav-links a {
  display: block;
  padding: var(--space-sm) var(--space-md);
  color: var(--color-text-secondary);
  font-size: var(--font-size-sm);
  font-weight: 500;
  border-radius: var(--radius-md);
  transition: all var(--transition);
  text-decoration: none;
  white-space: nowrap;
}

.nav-links a:hover,
.nav-links a.active {
  color: var(--color-primary);
  background-color: var(--color-primary-lighter);
}

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

/* Theme Toggle */
.theme-toggle {
  background: none;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: var(--space-sm);
  cursor: pointer;
  color: var(--color-text-secondary);
  display: flex;
  align-items: center;
  justify-content: center;
  width: 36px;
  height: 36px;
  transition: all var(--transition);
}

.theme-toggle:hover {
  color: var(--color-primary);
  border-color: var(--color-primary);
  background-color: var(--color-primary-lighter);
}

.theme-toggle .icon-sun,
.theme-toggle .icon-moon {
  width: 18px;
  height: 18px;
}

[data-theme="dark"] .theme-toggle .icon-sun { display: block; }
[data-theme="dark"] .theme-toggle .icon-moon { display: none; }
.theme-toggle .icon-sun { display: none; }
.theme-toggle .icon-moon { display: block; }

/* Hamburger Menu */
.nav-hamburger {
  display: none;
  background: none;
  border: none;
  cursor: pointer;
  padding: var(--space-sm);
  color: var(--color-text);
}

.nav-hamburger svg {
  width: 24px;
  height: 24px;
}

/* Mobile Navigation */
@media (max-width: 768px) {
  .nav-hamburger {
    display: flex;
    align-items: center;
  }

  .nav-links {
    display: none;
    position: absolute;
    top: var(--nav-height);
    left: 0;
    right: 0;
    background-color: var(--color-bg);
    border-bottom: 1px solid var(--color-border);
    flex-direction: column;
    padding: var(--space-md);
    gap: var(--space-xs);
    box-shadow: 0 4px 12px var(--color-shadow-lg);
  }

  [data-theme="dark"] .nav-links {
    background-color: var(--color-surface);
  }

  .nav-links.open {
    display: flex;
  }

  .nav-links a {
    width: 100%;
    padding: var(--space-md);
  }
}

/* --- Breadcrumb --- */
.breadcrumb {
  padding: var(--space-md) 0;
  font-size: var(--font-size-sm);
  color: var(--color-text-muted);
}

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

.breadcrumb span {
  margin: 0 var(--space-sm);
}

/* --- Hero Section --- */
.hero {
  background: linear-gradient(135deg, var(--color-primary-lighter) 0%, var(--color-bg) 50%, var(--color-surface) 100%);
  padding: var(--space-3xl) 0;
  text-align: center;
}

[data-theme="dark"] .hero {
  background: linear-gradient(135deg, var(--color-primary-lighter) 0%, var(--color-bg) 100%);
}

.hero-content {
  max-width: 800px;
  margin: 0 auto;
}

.hero h1 {
  font-size: var(--font-size-4xl);
  margin-bottom: var(--space-md);
  background: linear-gradient(135deg, var(--color-primary), var(--color-primary-dark));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.hero .subtitle {
  font-size: var(--font-size-xl);
  color: var(--color-text-secondary);
  margin-bottom: var(--space-xl);
}

.hero .disclaimer {
  display: inline-block;
  background: var(--color-warning-bg);
  color: #92400E;
  padding: var(--space-sm) var(--space-lg);
  border-radius: var(--radius-md);
  font-size: var(--font-size-sm);
  border: 1px solid #FDE68A;
}

[data-theme="dark"] .hero .disclaimer {
  color: #FCD34D;
  border-color: #78350F;
}

/* --- Cards --- */
.card {
  background: var(--color-card);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: var(--space-xl);
  transition: all var(--transition-slow);
  box-shadow: 0 1px 3px var(--color-shadow);
}

.card:hover {
  box-shadow: 0 4px 12px var(--color-shadow-lg);
  transform: translateY(-2px);
}

.card-grid {
  display: grid;
  gap: var(--space-xl);
}

.card-grid-2 {
  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
}

.card-grid-3 {
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
}

.card-grid-5 {
  grid-template-columns: repeat(auto-fill, minmax(220px, 1fr));
}

/* Quick Link Cards */
.quick-link-card {
  text-align: center;
  padding: var(--space-2xl);
  text-decoration: none;
  color: var(--color-text);
  display: block;
}

.quick-link-card:hover {
  text-decoration: none;
  border-color: var(--color-primary);
}

.quick-link-card .card-icon {
  font-size: 2.5rem;
  margin-bottom: var(--space-md);
}

.quick-link-card h3 {
  margin-bottom: var(--space-sm);
  color: var(--color-primary);
}

.quick-link-card p {
  color: var(--color-text-secondary);
  font-size: var(--font-size-sm);
}

/* Author Cards */
.author-card {
  text-align: center;
  padding: var(--space-xl);
}

.author-avatar {
  width: 72px;
  height: 72px;
  border-radius: 50%;
  background: linear-gradient(135deg, var(--color-primary), var(--color-primary-dark));
  display: flex;
  align-items: center;
  justify-content: center;
  margin: 0 auto var(--space-md);
  color: white;
  font-size: var(--font-size-2xl);
  font-weight: 700;
}

.author-card h3 {
  margin-bottom: var(--space-xs);
}

.author-card .author-en-name {
  color: var(--color-text-muted);
  font-size: var(--font-size-sm);
  margin-bottom: var(--space-sm);
}

.author-card .author-affiliation {
  color: var(--color-text-secondary);
  font-size: var(--font-size-sm);
  margin-bottom: var(--space-sm);
}

.author-card .author-email {
  font-size: var(--font-size-xs);
  color: var(--color-text-muted);
  word-break: break-all;
  margin-bottom: var(--space-sm);
}

.author-card .author-tags {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-xs);
  justify-content: center;
  margin-bottom: var(--space-md);
}

.tag {
  display: inline-block;
  padding: 2px 10px;
  background: var(--color-primary-lighter);
  color: var(--color-primary);
  border-radius: 999px;
  font-size: var(--font-size-xs);
  font-weight: 500;
}

[data-theme="dark"] .tag {
  background: var(--color-primary-light);
}

/* --- Buttons --- */
.btn {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-sm) var(--space-lg);
  border-radius: var(--radius-md);
  font-size: var(--font-size-sm);
  font-weight: 500;
  cursor: pointer;
  border: none;
  transition: all var(--transition);
  text-decoration: none;
  white-space: nowrap;
  font-family: var(--font-family);
  line-height: 1.5;
}

.btn:hover {
  text-decoration: none;
}

.btn:focus-visible {
  outline: 2px solid var(--color-primary);
  outline-offset: 2px;
}

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

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

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

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

.btn-sm {
  padding: 4px 12px;
  font-size: var(--font-size-xs);
}

.btn-lg {
  padding: var(--space-md) var(--space-2xl);
  font-size: var(--font-size-base);
}

.btn:disabled,
.btn.disabled {
  opacity: 0.5;
  cursor: not-allowed;
  pointer-events: none;
}

.btn-success {
  background: var(--color-success);
  color: #FFFFFF;
}

.btn-success:hover {
  background: #15803D;
  color: #FFFFFF;
}

/* --- Cover Section --- */
.cover-section {
  text-align: center;
}

.cover-image-wrapper {
  display: inline-block;
  max-width: 320px;
  cursor: pointer;
  border-radius: var(--radius-lg);
  overflow: hidden;
  box-shadow: 0 8px 24px var(--color-shadow-lg);
  transition: transform var(--transition-slow);
}

.cover-image-wrapper:hover {
  transform: scale(1.02);
}

.cover-image-wrapper img {
  width: 100%;
  display: block;
}

/* --- Purchase Section --- */
.purchase-section {
  text-align: center;
  padding: var(--space-2xl);
  background: var(--color-surface);
  border-radius: var(--radius-lg);
}

.purchase-section p {
  color: var(--color-text-secondary);
  margin-top: var(--space-md);
  font-size: var(--font-size-sm);
}

/* --- Solutions Page --- */
.solution-item {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--space-lg);
  background: var(--color-card);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  margin-bottom: var(--space-md);
  transition: all var(--transition);
  flex-wrap: wrap;
  gap: var(--space-md);
}

.solution-item:hover {
  border-color: var(--color-primary);
  box-shadow: 0 2px 8px var(--color-shadow);
}

.solution-info {
  display: flex;
  align-items: center;
  gap: var(--space-md);
  flex: 1;
  min-width: 200px;
}

.solution-chapter-num {
  background: var(--color-primary);
  color: white;
  width: 40px;
  height: 40px;
  border-radius: var(--radius-md);
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: var(--font-size-sm);
  flex-shrink: 0;
}

.solution-title {
  font-weight: 500;
}

.solution-actions {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  flex-wrap: wrap;
}

.status-badge {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  padding: 4px 12px;
  border-radius: 999px;
  font-size: var(--font-size-xs);
  font-weight: 500;
}

.status-badge.available {
  background: var(--color-success-bg);
  color: var(--color-success);
}

.status-badge.unavailable {
  background: var(--color-warning-bg);
  color: var(--color-warning);
}

/* --- Citation Page --- */
.citation-block {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: var(--space-xl);
  margin-bottom: var(--space-xl);
  position: relative;
}

.citation-block h3 {
  margin-bottom: var(--space-md);
}

.citation-block pre {
  background: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: var(--space-lg);
  overflow-x: auto;
  font-family: var(--font-mono);
  font-size: var(--font-size-sm);
  line-height: 1.6;
  white-space: pre-wrap;
  word-break: break-word;
}

.copy-btn {
  position: absolute;
  top: var(--space-lg);
  right: var(--space-lg);
}

/* --- Collapsible --- */
.collapsible-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--space-md) var(--space-lg);
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  cursor: pointer;
  font-weight: 500;
  transition: all var(--transition);
  user-select: none;
}

.collapsible-header:hover {
  background: var(--color-primary-lighter);
}

.collapsible-header .arrow {
  transition: transform var(--transition);
  font-size: var(--font-size-sm);
}

.collapsible-header.open .arrow {
  transform: rotate(90deg);
}

.collapsible-content {
  display: none;
  padding: var(--space-lg);
  border: 1px solid var(--color-border);
  border-top: none;
  border-radius: 0 0 var(--radius-md) var(--radius-md);
  background: var(--color-card);
}

.collapsible-content.open {
  display: block;
}

.collapsible-content ul {
  list-style: none;
  padding-left: var(--space-lg);
}

.collapsible-content li {
  padding: var(--space-xs) 0;
  position: relative;
}

.collapsible-content li::before {
  content: "·";
  position: absolute;
  left: calc(-1 * var(--space-md));
  color: var(--color-text-muted);
}

/* --- TOC Images --- */
.toc-images {
  display: flex;
  flex-direction: column;
  gap: var(--space-xl);
  align-items: center;
}

.toc-image-wrapper {
  max-width: 700px;
  width: 100%;
  cursor: pointer;
  border-radius: var(--radius-md);
  overflow: hidden;
  border: 1px solid var(--color-border);
  transition: all var(--transition);
}

.toc-image-wrapper:hover {
  box-shadow: 0 4px 12px var(--color-shadow-lg);
}

/* --- Image Modal --- */
.image-modal-overlay {
  display: none;
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: var(--color-overlay);
  z-index: 2000;
  align-items: center;
  justify-content: center;
  padding: var(--space-xl);
  cursor: pointer;
}

.image-modal-overlay.open {
  display: flex;
}

.image-modal-overlay img {
  max-width: 90vw;
  max-height: 90vh;
  object-fit: contain;
  border-radius: var(--radius-md);
  cursor: default;
}

.image-modal-close {
  position: fixed;
  top: var(--space-lg);
  right: var(--space-lg);
  background: rgba(255, 255, 255, 0.2);
  border: none;
  color: white;
  font-size: var(--font-size-2xl);
  cursor: pointer;
  width: 44px;
  height: 44px;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 2001;
  transition: background var(--transition);
}

.image-modal-close:hover {
  background: rgba(255, 255, 255, 0.4);
}

/* --- Feedback Page --- */
.feedback-list {
  list-style: none;
  padding: 0;
}

.feedback-list li {
  padding: var(--space-sm) 0;
  padding-left: var(--space-xl);
  position: relative;
  color: var(--color-text-secondary);
}

.feedback-list li::before {
  content: "•";
  position: absolute;
  left: var(--space-sm);
  color: var(--color-primary);
  font-weight: 700;
}

/* --- Acknowledgments --- */
.ack-group {
  margin-bottom: var(--space-2xl);
}

.ack-group h3 {
  margin-bottom: var(--space-md);
  color: var(--color-primary);
}

.ack-group ul {
  list-style: disc;
  padding-left: var(--space-xl);
}

.ack-group li {
  padding: var(--space-xs) 0;
  color: var(--color-text-secondary);
}

/* --- Footer --- */
.site-footer {
  margin-top: auto;
  background: var(--color-surface);
  border-top: 1px solid var(--color-border);
  padding: var(--space-2xl) 0;
  font-size: var(--font-size-sm);
  color: var(--color-text-secondary);
}

.footer-content {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  align-items: center;
  gap: var(--space-md);
}

.footer-links {
  display: flex;
  gap: var(--space-lg);
  flex-wrap: wrap;
}

.footer-links a {
  color: var(--color-text-secondary);
  font-size: var(--font-size-sm);
}

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

/* --- Page Content --- */
.page-content {
  padding: var(--space-2xl) 0 var(--space-3xl);
  flex: 1;
}

.page-header {
  margin-bottom: var(--space-2xl);
}

.page-header h1 {
  margin-bottom: var(--space-sm);
}

.page-header p {
  color: var(--color-text-secondary);
}

/* --- 404 Page --- */
.page-404 {
  text-align: center;
  padding: var(--space-3xl) 0;
}

.page-404 .error-code {
  font-size: 8rem;
  font-weight: 700;
  color: var(--color-primary);
  opacity: 0.3;
  line-height: 1;
}

.page-404 h1 {
  margin: var(--space-lg) 0;
}

.page-404 p {
  color: var(--color-text-secondary);
  margin-bottom: var(--space-xl);
}

/* --- Note Box --- */
.note-box {
  background: var(--color-primary-lighter);
  border-left: 4px solid var(--color-primary);
  padding: var(--space-lg);
  border-radius: 0 var(--radius-md) var(--radius-md) 0;
  margin: var(--space-xl) 0;
  font-size: var(--font-size-sm);
  color: var(--color-text-secondary);
}

[data-theme="dark"] .note-box {
  background: var(--color-primary-light);
}

/* --- Responsive --- */
@media (max-width: 640px) {
  :root {
    --font-size-3xl: 1.75rem;
    --font-size-4xl: 2rem;
  }

  .hero {
    padding: var(--space-2xl) 0;
  }

  .section {
    padding: var(--space-2xl) 0;
  }

  .card {
    padding: var(--space-lg);
  }

  .solution-item {
    flex-direction: column;
    align-items: flex-start;
  }

  .solution-actions {
    width: 100%;
    justify-content: flex-start;
  }

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

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

  .cover-image-wrapper {
    max-width: 240px;
  }
}

/* --- Print --- */
@media print {
  .navbar,
  .theme-toggle,
  .nav-hamburger,
  .image-modal-overlay {
    display: none !important;
  }

  body {
    color: #000;
    background: #fff;
  }
}