/* ===== Buttons ===== */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-sm);
  padding: var(--space-sm) var(--space-lg);
  border-radius: var(--radius-sm);
  font-size: 0.9rem;
  font-weight: 600;
  transition: all var(--transition-fast);
}

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

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

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

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

.btn-lg {
  padding: var(--space-md) var(--space-xl);
  font-size: 1rem;
  border-radius: var(--radius-md);
}

.btn-block {
  width: 100%;
}

.btn:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}

/* ===== Cards ===== */
.card {
  background: var(--color-surface);
  border-radius: var(--radius-card);
  box-shadow: 0 1px 3px var(--color-card-shadow);
  padding: var(--space-lg);
  margin-bottom: var(--space-md);
}

/* ===== Flashcard / 单词卡片 ===== */
.flashcard-container {
  perspective: 1200px;
  margin-bottom: var(--space-lg);
}

.flashcard {
  position: relative;
  width: 100%;
  min-height: 320px;
  cursor: pointer;
}

.flashcard-inner {
  position: relative;
  width: 100%;
  min-height: 320px;
  transition: transform 0.5s ease;
  transform-style: preserve-3d;
}

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

.flashcard-front,
.flashcard-back {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  min-height: 320px;
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;
  background: var(--color-surface);
  border-radius: var(--radius-card);
  box-shadow: 0 4px 20px var(--color-card-shadow);
  padding: var(--space-xl);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
}

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

.flashcard-word {
  font-size: 2rem;
  font-weight: 700;
  margin-bottom: var(--space-sm);
}

.flashcard-phonetic {
  font-size: 1rem;
  color: var(--color-text-secondary);
  margin-bottom: var(--space-md);
}

.flashcard-speak {
  font-size: 1.5rem;
  cursor: pointer;
  padding: var(--space-sm);
  border-radius: 50%;
  background: var(--color-primary-light);
  width: 48px;
  height: 48px;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: background var(--transition-fast);
}

.flashcard-speak:hover {
  background: var(--color-primary);
  color: white;
}

.flashcard-hint {
  color: var(--color-text-muted);
  font-size: 0.8rem;
  margin-top: var(--space-lg);
}

.flashcard-definition {
  font-size: 1.3rem;
  font-weight: 600;
  margin-bottom: var(--space-md);
  text-align: center;
}

.flashcard-example {
  font-family: var(--font-mono);
  font-size: 0.85rem;
  background: var(--color-bg);
  border-radius: var(--radius-sm);
  padding: var(--space-md);
  width: 100%;
  white-space: pre-wrap;
  word-break: break-all;
  line-height: 1.5;
  margin-bottom: var(--space-sm);
  color: var(--color-text-secondary);
}

.flashcard-explain {
  font-size: 0.85rem;
  color: var(--color-text-secondary);
  text-align: center;
}

@media (max-width: 480px) {
  .flashcard-word { font-size: 1.6rem; }
  .flashcard-definition { font-size: 1.1rem; }
  .flashcard-front, .flashcard-back { min-height: 260px; padding: var(--space-lg); }
  .flashcard-inner { min-height: 260px; }
}

/* ===== Rating buttons (SM-2) ===== */
.rating-group {
  display: flex;
  gap: var(--space-sm);
  justify-content: center;
  flex-wrap: wrap;
}

.rating-btn {
  width: 52px;
  height: 52px;
  border-radius: 50%;
  font-weight: 700;
  font-size: 1rem;
  border: 2px solid var(--color-border);
  background: var(--color-surface);
  transition: all var(--transition-fast);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  line-height: 1.2;
}

.rating-btn .rating-label {
  font-size: 0.55rem;
  font-weight: 400;
  color: var(--color-text-muted);
}

.rating-btn:hover {
  transform: scale(1.1);
}

.rating-btn[data-score="0"]:hover { border-color: #ef4444; color: #ef4444; }
.rating-btn[data-score="1"]:hover { border-color: #f97316; color: #f97316; }
.rating-btn[data-score="2"]:hover { border-color: #f59e0b; color: #f59e0b; }
.rating-btn[data-score="3"]:hover { border-color: #84cc16; color: #84cc16; }
.rating-btn[data-score="4"]:hover { border-color: #22c55e; color: #22c55e; }
.rating-btn[data-score="5"]:hover { border-color: #10b981; color: #10b981; }

/* ===== Progress bars ===== */
.progress-bar {
  width: 100%;
  height: 8px;
  background: var(--color-bg);
  border-radius: 4px;
  overflow: hidden;
}

.progress-bar-fill {
  height: 100%;
  border-radius: 4px;
  background: var(--color-primary);
  transition: width var(--transition-normal);
}

/* ===== Stat cards ===== */
.stats-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(140px, 1fr));
  gap: var(--space-md);
}

.stat-card {
  background: var(--color-surface);
  border-radius: var(--radius-md);
  padding: var(--space-md);
  text-align: center;
  box-shadow: 0 1px 3px var(--color-card-shadow);
}

.stat-value {
  font-size: 1.8rem;
  font-weight: 700;
  color: var(--color-primary);
}

.stat-label {
  font-size: 0.8rem;
  color: var(--color-text-secondary);
  margin-top: var(--space-xs);
}

/* ===== Tier list ===== */
.tier-item {
  display: flex;
  align-items: center;
  gap: var(--space-md);
  padding: var(--space-md) 0;
}

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

.tier-info {
  flex: 1;
}

.tier-name {
  font-weight: 600;
  font-size: 0.95rem;
}

.tier-count {
  font-size: 0.8rem;
  color: var(--color-text-muted);
}

.tier-status {
  font-size: 0.8rem;
  font-weight: 500;
}

.tier-status.locked { color: var(--color-text-muted); }
.tier-status.active { color: var(--color-primary); }
.tier-status.done { color: var(--color-success); }

/* ===== Word list ===== */
.wordlist-controls {
  display: flex;
  gap: var(--space-sm);
  margin-bottom: var(--space-md);
  flex-wrap: wrap;
}

.wordlist-controls input {
  flex: 1;
  min-width: 160px;
}

.wordlist-controls select {
  min-width: 90px;
}

.wordlist-table {
  width: 100%;
  border-collapse: collapse;
}

.wordlist-row {
  display: grid;
  grid-template-columns: 32px 1fr auto auto;
  gap: var(--space-sm);
  align-items: center;
  padding: var(--space-sm) var(--space-md);
  border-bottom: 1px solid var(--color-border);
  font-size: 0.85rem;
}

.wordlist-row:hover {
  background: var(--color-primary-light);
}

.wordlist-row .status-dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
}

.wordlist-row .status-dot.new { background: var(--color-text-muted); }
.wordlist-row .status-dot.learning { background: var(--color-warning); }
.wordlist-row .status-dot.mastered { background: var(--color-success); }

.wordlist-word {
  font-weight: 600;
}

.wordlist-def {
  color: var(--color-text-secondary);
  font-size: 0.8rem;
}

.wordlist-tier-badge {
  font-size: 0.7rem;
  padding: 2px 8px;
  border-radius: 10px;
  background: var(--color-primary-light);
  color: var(--color-primary);
}

.pagination {
  display: flex;
  justify-content: center;
  gap: var(--space-xs);
  margin-top: var(--space-md);
}

.pagination button {
  padding: var(--space-xs) var(--space-sm);
  border-radius: var(--radius-sm);
  border: 1px solid var(--color-border);
  font-size: 0.8rem;
  min-width: 32px;
}

.pagination button.active {
  background: var(--color-primary);
  color: white;
  border-color: var(--color-primary);
}

/* ===== Empty state ===== */
.empty-state {
  text-align: center;
  padding: var(--space-xl) var(--space-md);
  color: var(--color-text-muted);
}

.empty-state-icon {
  font-size: 3rem;
  margin-bottom: var(--space-md);
}

.empty-state-text {
  font-size: 0.95rem;
  margin-bottom: var(--space-lg);
}

/* ===== Settings ===== */
.settings-group {
  margin-bottom: var(--space-lg);
}

.settings-group-title {
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--color-text-secondary);
  text-transform: uppercase;
  letter-spacing: 0.5px;
  margin-bottom: var(--space-md);
}

.setting-item {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--space-sm) 0;
}

.setting-label {
  font-size: 0.9rem;
}

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

/* Toggle switch */
.toggle {
  position: relative;
  width: 44px;
  height: 24px;
  flex-shrink: 0;
}

.toggle input {
  opacity: 0;
  width: 0;
  height: 0;
}

.toggle-slider {
  position: absolute;
  cursor: pointer;
  top: 0; left: 0; right: 0; bottom: 0;
  background: var(--color-border);
  border-radius: 12px;
  transition: var(--transition-fast);
}

.toggle-slider::before {
  content: '';
  position: absolute;
  height: 18px;
  width: 18px;
  left: 3px;
  bottom: 3px;
  background: white;
  border-radius: 50%;
  transition: var(--transition-fast);
}

.toggle input:checked + .toggle-slider {
  background: var(--color-primary);
}

.toggle input:checked + .toggle-slider::before {
  transform: translateX(20px);
}

/* ===== Session progress ===== */
.session-progress {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  font-size: 0.8rem;
  color: var(--color-text-muted);
  margin-bottom: var(--space-md);
}

.session-progress-bar {
  flex: 1;
  height: 4px;
  background: var(--color-border);
  border-radius: 2px;
  overflow: hidden;
}

.session-progress-fill {
  height: 100%;
  background: var(--color-primary);
  border-radius: 2px;
  transition: width var(--transition-normal);
}

/* ===== Review history bar chart ===== */
.chart-bars {
  display: flex;
  align-items: flex-end;
  gap: 4px;
  height: 120px;
  padding: var(--space-sm) 0;
}

.chart-bar {
  flex: 1;
  border-radius: 4px 4px 0 0;
  background: var(--color-primary);
  opacity: 0.7;
  min-height: 4px;
  transition: height var(--transition-normal);
}

.chart-bar:hover {
  opacity: 1;
}

/* ===== Danger zone ===== */
.danger-zone {
  border: 1px solid var(--color-danger);
  border-radius: var(--radius-md);
  padding: var(--space-md);
}

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

/* ===== Toast notification ===== */
.toast {
  position: fixed;
  top: calc(var(--header-height) + var(--space-sm));
  left: 50%;
  transform: translateX(-50%);
  background: var(--color-text);
  color: var(--color-bg);
  padding: var(--space-sm) var(--space-lg);
  border-radius: var(--radius-sm);
  font-size: 0.85rem;
  z-index: 200;
  animation: toastIn 0.3s ease;
  pointer-events: none;
}

@keyframes toastIn {
  from { opacity: 0; transform: translateX(-50%) translateY(-10px); }
  to { opacity: 1; transform: translateX(-50%) translateY(0); }
}