/* Design System Tokens — 涯涯背单词 */
@import url('https://fonts.googleapis.com/css2?family=Nunito:wght@400;600;700;800&family=Noto+Sans+SC:wght@400;500;700&display=swap');

:root {
  /* Typography */
  --font-heading: 'Nunito', 'Noto Sans SC', -apple-system, sans-serif;
  --font-body: 'Noto Sans SC', 'Nunito', -apple-system, sans-serif;

  /* Primary palette: purple-indigo family */
  --color-primary: #6c3ce0;
  --color-primary-light: #8b5cf6;
  --color-primary-dark: #4c1d95;
  --color-secondary: #818cf8;
  --color-accent: #a78bfa;

  /* Gradients — unified across all pages */
  --gradient-main: linear-gradient(135deg, #6c3ce0 0%, #4338ca 50%, #3b82f6 100%);
  --gradient-shop: linear-gradient(135deg, #6c3ce0 0%, #7c3aed 50%, #8b5cf6 100%);
  --gradient-card: linear-gradient(135deg, rgba(255,255,255,0.15), rgba(255,255,255,0.05));

  /* Text */
  --color-text: #ffffff;
  --color-text-secondary: rgba(255, 255, 255, 0.8);
  --color-text-muted: rgba(255, 255, 255, 0.6);
  --color-text-dark: #1e1b4b;

  /* Surfaces */
  --color-surface: rgba(255, 255, 255, 0.15);
  --color-surface-hover: rgba(255, 255, 255, 0.25);
  --color-card: rgba(255, 255, 255, 0.95);

  /* Feedback */
  --color-success: #34d399;
  --color-error: #f87171;
  --color-warning: #fbbf24;

  /* Spacing tokens */
  --space-xs: 4px;
  --space-sm: 8px;
  --space-md: 16px;
  --space-lg: 24px;
  --space-xl: 32px;

  /* Border radius tokens */
  --radius-sm: 8px;
  --radius-md: 12px;
  --radius-lg: 20px;
  --radius-pill: 9999px;

  /* Shadows */
  --shadow-card: 0 2px 8px rgba(0, 0, 0, 0.08), 0 1px 2px rgba(0, 0, 0, 0.04);
  --shadow-card-hover: 0 8px 24px rgba(0, 0, 0, 0.12), 0 2px 4px rgba(0, 0, 0, 0.06);
  --shadow-elevated: 0 12px 40px rgba(0, 0, 0, 0.15);
}

/* Skeleton loading animation */
@keyframes skeleton-shimmer {
  0% { background-position: -200% 0; }
  100% { background-position: 200% 0; }
}

.skeleton {
  background: linear-gradient(90deg, rgba(255,255,255,0.1) 25%, rgba(255,255,255,0.25) 50%, rgba(255,255,255,0.1) 75%);
  background-size: 200% 100%;
  animation: skeleton-shimmer 1.5s ease-in-out infinite;
  border-radius: var(--radius-sm);
}

.skeleton-text {
  height: 14px;
  width: 80%;
  margin-bottom: 8px;
  background: linear-gradient(90deg, rgba(255,255,255,0.1) 25%, rgba(255,255,255,0.25) 50%, rgba(255,255,255,0.1) 75%);
  background-size: 200% 100%;
  animation: skeleton-shimmer 1.5s ease-in-out infinite;
  border-radius: 4px;
}

/* Empty state styling */
.empty-state {
  text-align: center;
  padding: var(--space-lg) var(--space-md);
  opacity: 0.7;
  color: var(--color-text-muted);
  font-size: 0.9rem;
}

.empty-state .empty-emoji {
  font-size: 2.5rem;
  margin-bottom: var(--space-sm);
  display: block;
}

.placeholder {
  opacity: 0.5;
  animation: skeleton-shimmer 2s ease-in-out infinite;
  background: linear-gradient(90deg, transparent 25%, rgba(255,255,255,0.15) 50%, transparent 75%);
  background-size: 200% 100%;
  -webkit-background-clip: text;
}

/* Error state styling */
.error-state {
  text-align: center;
  padding: var(--space-lg) var(--space-md);
  color: var(--color-error);
  font-size: 0.9rem;
  border-radius: var(--radius-md);
  background: rgba(248, 113, 113, 0.1);
}

.error-state .error-emoji {
  font-size: 2rem;
  margin-bottom: var(--space-sm);
  display: block;
}

.retry-btn {
  margin-top: var(--space-sm);
  padding: var(--space-sm) var(--space-md);
  border: 2px solid var(--color-error);
  background: transparent;
  color: var(--color-error);
  border-radius: var(--radius-sm);
  font-size: 0.85rem;
  font-weight: 600;
  cursor: pointer;
  transition: background 0.2s;
}

.retry-btn:hover {
  background: rgba(248, 113, 113, 0.15);
}

.skeleton-card {
  height: 80px;
  width: 100%;
  margin-bottom: var(--space-sm);
  background: linear-gradient(90deg, rgba(255,255,255,0.08) 25%, rgba(255,255,255,0.18) 50%, rgba(255,255,255,0.08) 75%);
  background-size: 200% 100%;
  animation: skeleton-shimmer 1.5s ease-in-out infinite;
  border-radius: var(--radius-md);
}

/* Keyboard accessibility: focus indicators */
*:focus-visible {
  outline: 2px solid #fbbf24;
  outline-offset: 2px;
}

button:focus-visible,
a:focus-visible,
input:focus-visible,
select:focus-visible {
  outline: 2px solid #fbbf24;
  outline-offset: 2px;
  box-shadow: 0 0 0 4px rgba(251, 191, 36, 0.3);
}

/* Responsive: Mobile */
@media (max-width: 640px) {
  :root {
    --space-lg: 16px;
    --space-xl: 24px;
  }

  body {
    padding: var(--space-md) !important;
  }

  .score-bar {
    flex-direction: column;
    align-items: stretch;
  }

  .score-card {
    min-width: auto;
  }

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

  .app-nav {
    gap: var(--space-xs) !important;
  }

  .app-nav a,
  .app-nav button {
    font-size: 0.78rem;
    padding: 8px 10px;
    min-height: 44px;
    display: flex;
    align-items: center;
  }

  input[type="text"],
  input[type="search"],
  input[type="email"] {
    width: 100%;
    font-size: 16px; /* prevent iOS zoom */
    min-height: 44px;
  }

  .header h1 {
    font-size: 1.6rem;
  }
}