:root {
  --color-accent: #FBBF24;
  --color-accent-dark: #F59E0B;
  --color-success: #10B981;
  --color-error: #EF4444;
  --color-text: #0F172A;
  --color-text-secondary: #64748B;
  --color-text-tertiary: #94A3B8;
  --color-bg: #FFFFFF;
  --color-bg-secondary: #F8FAFC;
  --color-bg-hover: #F8FAFC;
  --color-border: #E2E8F0;
  --font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  --shadow-sm: 0 1px 2px 0 rgba(0,0,0,0.02);
  --shadow-md: 0 2px 8px 0 rgba(0,0,0,0.04);
  --shadow-lg: 0 4px 16px 0 rgba(0,0,0,0.06);
  --radius: 8px;
  --radius-lg: 12px;
  --transition: 200ms cubic-bezier(0.4, 0, 0.2, 1);
}

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

body {
  font-family: var(--font-family);
  color: var(--color-text);
  background: var(--color-bg);
  line-height: 1.6;
  font-size: 1rem;
  -webkit-font-smoothing: antialiased;
}

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

/* Nav */
.nav {
  border-bottom: 1px solid var(--color-border);
  padding: 16px 0;
  background: white;
  position: sticky;
  top: 0;
  z-index: 100;
}

.nav-container {
  display: flex;
  justify-content: space-between;
  align-items: center;
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 24px;
}

.nav-brand {
  font-weight: 600;
  color: var(--color-text);
  font-size: 1.125rem;
  text-decoration: none;
  transition: color var(--transition);
}

.nav-brand:hover { color: var(--color-accent-dark); }

.nav-links { display: flex; gap: 24px; align-items: center; }

.nav-link {
  color: var(--color-text-secondary);
  font-weight: 500;
  transition: color var(--transition);
  font-size: 0.9375rem;
}

.nav-link:hover, .nav-link.active { color: var(--color-text); }

/* Containers */
.container { max-width: 800px; margin: 0 auto; padding: 0 24px; }
.container-wide { max-width: 1200px; margin: 0 auto; padding: 0 24px; }

/* Hero */
.hero {
  min-height: 90vh;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 96px 24px;
  text-align: center;
}

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

.hero-title {
  font-size: 3.5rem;
  font-weight: 700;
  line-height: 1.1;
  letter-spacing: -0.02em;
  margin-bottom: 24px;
}

.hero-title .accent { color: var(--color-accent-dark); }

.hero-subtitle {
  font-size: 1.25rem;
  color: var(--color-text-secondary);
  margin-bottom: 48px;
  max-width: 600px;
  margin-left: auto;
  margin-right: auto;
}

/* Demo Animation */
.demo-container {
  background: var(--color-bg-secondary);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 32px;
  margin-bottom: 48px;
  min-height: 120px;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  transition: all 0.5s ease;
}

.demo-word {
  font-size: 1.5rem;
  font-weight: 600;
  margin-bottom: 8px;
  font-family: 'Courier New', monospace;
}

.demo-meaning {
  font-size: 1rem;
  color: var(--color-text-secondary);
}

/* Buttons */
.btn {
  padding: 12px 24px;
  border-radius: var(--radius);
  font-weight: 600;
  transition: all var(--transition);
  cursor: pointer;
  border: none;
  font-size: 1rem;
  font-family: var(--font-family);
  display: inline-flex;
  align-items: center;
  gap: 8px;
}

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

.btn-primary:hover {
  transform: translateY(-2px);
  box-shadow: 0 4px 12px rgba(251, 191, 36, 0.3);
  background: var(--color-accent-dark);
}

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

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

.btn-large { padding: 16px 32px; font-size: 1.125rem; }

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

.btn-success:hover {
  transform: translateY(-2px);
  box-shadow: 0 4px 12px rgba(16, 185, 129, 0.3);
}

.cta-group { display: flex; gap: 16px; justify-content: center; flex-wrap: wrap; }

/* Stats */
.stat-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 32px;
  margin: 96px auto;
  max-width: 800px;
  padding: 0 24px;
}

.stat-card { text-align: center; padding: 32px 16px; }

.stat-value {
  font-size: 3rem;
  font-weight: 700;
  color: var(--color-text);
  line-height: 1;
}

.stat-label {
  font-size: 1rem;
  color: var(--color-text-secondary);
  margin-top: 8px;
}

/* Footer */
.site-footer {
  border-top: 1px solid var(--color-border);
  padding: 64px 24px;
  text-align: center;
}

.footer-tagline {
  font-size: 1.5rem;
  font-weight: 600;
  margin-bottom: 16px;
}

.footer-description {
  color: var(--color-text-secondary);
  max-width: 600px;
  margin: 0 auto;
  line-height: 1.8;
}

/* Cards */
.card {
  background: white;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 24px;
  transition: all var(--transition);
}

.card:hover {
  border-color: var(--color-accent);
  box-shadow: var(--shadow-md);
}

/* Root Cards Grid */
.roots-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 20px;
  margin-top: 24px;
}

.root-card {
  background: white;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 20px;
  cursor: pointer;
  transition: all var(--transition);
  position: relative;
}

.root-card:hover {
  border-color: var(--color-accent);
  box-shadow: var(--shadow-md);
  transform: translateY(-2px);
}

.root-card.mastered { border-left: 3px solid var(--color-success); }

.root-name {
  font-size: 1.125rem;
  font-weight: 600;
  margin-bottom: 8px;
  font-family: 'Courier New', monospace;
}

.root-meaning {
  color: var(--color-text-secondary);
  font-size: 0.9375rem;
  margin-bottom: 8px;
}

.root-origin {
  display: inline-block;
  background: var(--color-accent);
  color: var(--color-text);
  padding: 4px 12px;
  border-radius: var(--radius);
  font-size: 0.8125rem;
}

.mastered-badge {
  display: inline-block;
  background: var(--color-success);
  color: white;
  padding: 2px 8px;
  border-radius: var(--radius);
  font-size: 0.75rem;
  margin-left: 8px;
}

/* Search & Filters */
.search-bar {
  display: flex;
  gap: 12px;
  margin-bottom: 24px;
  flex-wrap: wrap;
}

.search-input {
  flex: 1;
  min-width: 200px;
  padding: 12px 16px;
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  font-size: 1rem;
  font-family: var(--font-family);
  transition: border-color var(--transition);
  outline: none;
}

.search-input:focus { border-color: var(--color-accent); }

.filter-btn {
  padding: 8px 16px;
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  background: white;
  cursor: pointer;
  font-size: 0.875rem;
  font-family: var(--font-family);
  transition: all var(--transition);
  color: var(--color-text-secondary);
}

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

/* Page Header */
.page-header {
  padding: 48px 0 32px;
  text-align: center;
}

.page-header h1 {
  font-size: 2rem;
  font-weight: 700;
  margin-bottom: 8px;
}

.page-header p {
  color: var(--color-text-secondary);
  font-size: 1.125rem;
}

/* Flashcard */
.flashcard-container {
  perspective: 1000px;
  max-width: 600px;
  margin: 0 auto;
}

.flashcard {
  width: 100%;
  min-height: 350px;
  cursor: pointer;
  position: relative;
  transform-style: preserve-3d;
  transition: transform 0.6s ease;
}

.flashcard.flipped { transform: rotateY(180deg); }

.flashcard-front, .flashcard-back {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  min-height: 350px;
  backface-visibility: hidden;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 48px 32px;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  text-align: center;
  background: white;
}

.flashcard-back { transform: rotateY(180deg); }

.flashcard-root {
  font-size: 1.75rem;
  font-weight: 700;
  margin-bottom: 16px;
  font-family: 'Courier New', monospace;
}

.flashcard-meaning {
  font-size: 1.125rem;
  color: var(--color-text-secondary);
  margin-bottom: 12px;
}

.flashcard-origin {
  display: inline-block;
  background: var(--color-accent);
  padding: 4px 12px;
  border-radius: var(--radius);
  font-size: 0.8125rem;
}

.flashcard-description {
  font-size: 1rem;
  line-height: 1.8;
  color: var(--color-text-secondary);
  max-width: 500px;
}

/* Flashcard Controls */
.flashcard-controls {
  display: flex;
  justify-content: center;
  align-items: center;
  gap: 16px;
  margin-top: 32px;
}

.flashcard-progress {
  text-align: center;
  margin-top: 24px;
  color: var(--color-text-secondary);
}

.progress-bar-container {
  width: 100%;
  max-width: 400px;
  height: 4px;
  background: var(--color-border);
  border-radius: 2px;
  margin: 12px auto 0;
  overflow: hidden;
}

.progress-bar {
  height: 100%;
  background: var(--color-accent);
  border-radius: 2px;
  transition: width var(--transition);
}

/* Learn Page */
.learn-container { max-width: 700px; margin: 0 auto; padding: 32px 24px; }

.learn-header {
  margin-bottom: 32px;
  padding-bottom: 24px;
  border-bottom: 1px solid var(--color-border);
}

.learn-title {
  font-size: 2rem;
  font-weight: 700;
  margin-bottom: 8px;
  font-family: 'Courier New', monospace;
}

.learn-meta {
  display: flex;
  gap: 12px;
  align-items: center;
  flex-wrap: wrap;
}

.learn-description {
  font-size: 1.0625rem;
  line-height: 1.8;
  color: var(--color-text-secondary);
  margin-bottom: 32px;
}

.learn-section { margin-bottom: 32px; }

.learn-section h3 {
  font-size: 1.25rem;
  font-weight: 600;
  margin-bottom: 16px;
}

/* Examples */
.example-card {
  background: var(--color-bg-secondary);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 20px;
  margin-bottom: 12px;
}

.example-word {
  font-weight: 600;
  font-size: 1.0625rem;
  margin-bottom: 4px;
}

.example-meaning {
  color: var(--color-text-secondary);
  font-size: 0.9375rem;
  margin-bottom: 8px;
}

.example-explanation {
  font-size: 0.9375rem;
  line-height: 1.7;
}

/* Quiz */
.quiz-section {
  background: var(--color-bg-secondary);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 24px;
  margin-top: 32px;
}

.quiz-question {
  font-size: 1.0625rem;
  font-weight: 600;
  margin-bottom: 16px;
}

.quiz-options { display: flex; flex-direction: column; gap: 8px; }

.quiz-option {
  padding: 12px 16px;
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  background: white;
  cursor: pointer;
  font-size: 1rem;
  font-family: var(--font-family);
  text-align: left;
  transition: all var(--transition);
}

.quiz-option:hover:not(:disabled) {
  border-color: var(--color-accent);
  background: #FFFBEB;
}

.quiz-option:disabled { cursor: not-allowed; opacity: 0.8; }
.quiz-option.correct { background: #D1FAE5; border-color: var(--color-success); }
.quiz-option.wrong { background: #FEE2E2; border-color: var(--color-error); }

/* Learn Navigation */
.learn-nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-top: 48px;
  padding-top: 24px;
  border-top: 1px solid var(--color-border);
}

/* Progress Page */
.progress-overview {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  gap: 24px;
  margin-bottom: 48px;
}

.progress-stat {
  text-align: center;
  padding: 32px 16px;
  background: var(--color-bg-secondary);
  border-radius: var(--radius-lg);
  border: 1px solid var(--color-border);
}

.progress-stat .stat-value {
  font-size: 2.5rem;
  font-weight: 700;
}

.progress-stat .stat-label {
  margin-top: 8px;
  color: var(--color-text-secondary);
}

.progress-bar-large {
  width: 100%;
  height: 8px;
  background: var(--color-border);
  border-radius: 4px;
  overflow: hidden;
  margin-bottom: 48px;
}

.progress-bar-large .fill {
  height: 100%;
  background: var(--color-accent);
  border-radius: 4px;
  transition: width 0.5s ease;
}

.mastered-list { margin-top: 24px; }

.mastered-item {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 16px 0;
  border-bottom: 1px solid var(--color-border);
}

.mastered-item:last-child { border-bottom: none; }

.mastered-info h4 {
  font-size: 1rem;
  font-weight: 600;
  margin-bottom: 4px;
  font-family: 'Courier New', monospace;
}

.mastered-info p {
  color: var(--color-text-secondary);
  font-size: 0.875rem;
}

/* Detail Page */
.detail-container { max-width: 700px; margin: 0 auto; padding: 32px 24px; }

.detail-back {
  color: var(--color-text-secondary);
  font-size: 0.9375rem;
  margin-bottom: 24px;
  display: inline-block;
  transition: color var(--transition);
}

.detail-back:hover { color: var(--color-text); }

/* Feedback Toast */
.feedback-toast {
  position: fixed;
  bottom: 24px;
  left: 50%;
  transform: translateX(-50%);
  padding: 12px 24px;
  border-radius: var(--radius);
  font-weight: 500;
  font-size: 0.9375rem;
  z-index: 1000;
  animation: toast-in 0.3s ease, toast-out 0.3s ease 2.7s forwards;
  box-shadow: var(--shadow-lg);
}

.feedback-toast.success { background: var(--color-success); color: white; }
.feedback-toast.error { background: var(--color-error); color: white; }

@keyframes toast-in {
  from { opacity: 0; transform: translateX(-50%) translateY(20px); }
  to { opacity: 1; transform: translateX(-50%) translateY(0); }
}

@keyframes toast-out {
  from { opacity: 1; }
  to { opacity: 0; }
}

/* Keyboard hint */
.keyboard-hint {
  text-align: center;
  color: var(--color-text-tertiary);
  font-size: 0.8125rem;
  margin-top: 16px;
}

.keyboard-hint kbd {
  display: inline-block;
  padding: 2px 6px;
  background: var(--color-bg-secondary);
  border: 1px solid var(--color-border);
  border-radius: 4px;
  font-family: 'Courier New', monospace;
  font-size: 0.75rem;
}

/* Empty State */
.empty-state {
  text-align: center;
  padding: 64px 24px;
  color: var(--color-text-secondary);
}

.empty-state h3 {
  font-size: 1.25rem;
  margin-bottom: 8px;
  color: var(--color-text);
}

/* Toast (新版) */
.toast {
  position: fixed;
  bottom: 32px;
  left: 50%;
  transform: translateX(-50%) translateY(100px);
  background: #1a1a1a;
  color: white;
  padding: 12px 24px;
  border-radius: var(--radius-lg);
  font-size: 0.875rem;
  font-weight: 500;
  z-index: 1000;
  opacity: 0;
  transition: all 0.3s ease;
  pointer-events: none;
}

.toast.show {
  transform: translateX(-50%) translateY(0);
  opacity: 1;
}

/* Quiz Result */
.quiz-result {
  margin-top: 20px;
  padding: 16px;
  border-radius: var(--radius);
  font-weight: 500;
}

.quiz-result.correct {
  background: #D1FAE5;
  color: #065F46;
}

.quiz-result.incorrect {
  background: #FEE2E2;
  color: #991B1B;
}

.quiz-result.hidden {
  display: none;
}

/* Detail Meaning */
.detail-meaning {
  font-size: 1.125rem;
  color: var(--color-text-secondary);
  font-style: italic;
  margin-top: 16px;
  padding: 20px;
  background: var(--color-bg-secondary);
  border-radius: var(--radius-lg);
}

/* Learn Mastered Toggle */
.learn-mastered-toggle {
  text-align: center;
}

.learn-mastered-toggle label {
  display: flex;
  align-items: center;
  gap: 8px;
  cursor: pointer;
  font-size: 0.9375rem;
  color: var(--color-text-secondary);
}

.learn-mastered-toggle input[type="checkbox"] {
  width: 18px;
  height: 18px;
  cursor: pointer;
}

/* Demo Section (首页卡片预览) */
.demo-section {
  margin: 64px auto;
  max-width: 1000px;
  padding: 0 24px;
  text-align: center;
}

.demo-section-title {
  font-size: 1.75rem;
  font-weight: 600;
  margin-bottom: 40px;
}

.demo-cards {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 20px;
}

.demo-card {
  background: white;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 20px;
  cursor: pointer;
  transition: all var(--transition);
  text-align: left;
  opacity: 0;
  transform: translateY(20px);
  animation: fadeInUp 0.6s ease forwards;
}

.demo-card:hover {
  border-color: var(--color-accent);
  box-shadow: var(--shadow-md);
  transform: translateY(-2px);
}

@keyframes fadeInUp {
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.demo-card-header {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  margin-bottom: 12px;
}

.demo-card-title {
  font-weight: 600;
  font-size: 1rem;
  line-height: 1.4;
  font-family: 'Courier New', monospace;
}

.demo-card-category {
  background: var(--color-accent);
  color: var(--color-text);
  padding: 4px 8px;
  border-radius: 6px;
  font-size: 0.75rem;
  font-weight: 500;
  white-space: nowrap;
  margin-left: 8px;
}

.demo-card-description {
  color: var(--color-text-secondary);
  font-size: 0.875rem;
  line-height: 1.5;
}

/* Root description in index */
.root-desc {
  color: var(--color-text-secondary);
  font-size: 0.875rem;
  line-height: 1.5;
  display: -webkit-box;
  -webkit-line-clamp: 3;
  -webkit-box-orient: vertical;
  overflow: hidden;
  margin-bottom: 4px;
}

/* Filter group */
.filter-group {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  justify-content: center;
}

/* Ghost button */
.btn-ghost {
  background: transparent;
  color: var(--color-text-secondary);
  border: none;
}

.btn-ghost:hover {
  background: var(--color-bg-secondary);
  color: var(--color-text);
}

/* Text utilities */
.text-center { text-align: center; }
.hidden { display: none; }

/* Mobile hamburger */
.nav-toggle {
  display: none;
  background: none;
  border: none;
  cursor: pointer;
  padding: 4px;
}

.nav-toggle span {
  display: block;
  width: 24px;
  height: 2px;
  background: var(--color-text);
  margin: 5px 0;
  transition: var(--transition);
}

/* Responsive */
@media (max-width: 768px) {
  .hero-title { font-size: 2.25rem; }
  .hero-subtitle { font-size: 1.0625rem; }
  .hero { padding: 64px 16px; min-height: auto; }
  .stat-grid { grid-template-columns: 1fr; gap: 16px; margin: 48px auto; }
  .progress-overview { grid-template-columns: 1fr; }
  .roots-grid { grid-template-columns: 1fr; }
  .nav-toggle { display: block; }
  .nav-links {
    display: none;
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    background: white;
    border-bottom: 1px solid var(--color-border);
    flex-direction: column;
    padding: 16px 24px;
    gap: 16px;
  }
  .nav-links.open { display: flex; }
  .flashcard-front, .flashcard-back { padding: 32px 20px; min-height: 300px; }
  .flashcard { min-height: 300px; }
  .cta-group { flex-direction: column; align-items: center; }
}

@media (max-width: 480px) {
  .hero-title { font-size: 1.875rem; }
  .container-wide { padding: 0 16px; }
}