:root {
  --bg: #f7f7fb;
  --surface: #ffffff;
  --text: #1f2430;
  --muted: #6b7280;
  --primary: #4f46e5;
  --success: #16a34a;
  --danger: #dc2626;
  --border: #e5e7eb;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #14161f;
    --surface: #1e2130;
    --text: #f1f2f6;
    --muted: #9aa0ac;
    --border: #30354a;
  }
}

* { box-sizing: border-box; }

body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "PingFang SC", "Microsoft YaHei", sans-serif;
  background: var(--bg);
  color: var(--text);
}

.app-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 12px 16px;
  background: var(--surface);
  border-bottom: 1px solid var(--border);
  position: sticky;
  top: 0;
  z-index: 10;
}
.app-header h1 { font-size: 1.1rem; margin: 0; }
.app-header nav { display: flex; align-items: center; gap: 10px; }

.network-badge { font-size: 0.75rem; color: var(--muted); }
.network-badge.offline { color: var(--danger); }

button {
  font: inherit;
  border-radius: 8px;
  border: 1px solid var(--border);
  padding: 8px 14px;
  background: var(--surface);
  color: var(--text);
  cursor: pointer;
}
button.link { border: none; background: none; color: var(--primary); padding: 4px 8px; }
a.link { color: var(--primary); padding: 4px 8px; text-decoration: none; font: inherit; }
button.primary { background: var(--primary); color: #fff; border-color: var(--primary); }
button.secondary { background: var(--bg); }
button.success { background: var(--success); color: #fff; border-color: var(--success); }
button.danger { background: var(--danger); color: #fff; border-color: var(--danger); }
button.wide { flex: 1; padding: 14px; font-size: 1rem; }
button:disabled { opacity: 0.5; cursor: not-allowed; }

main {
  max-width: 720px;
  margin: 0 auto;
  padding: 16px;
  padding-bottom: 60px;
}

.hidden { display: none !important; }

.section-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  margin-bottom: 12px;
  flex-wrap: wrap;
}

.hint { color: var(--muted); font-size: 0.85rem; }
.hint.center { text-align: center; }

.category-header {
  margin: 0 0 14px;
  color: var(--text);
  font-size: 1.05rem;
  font-weight: 600;
  display: flex;
  align-items: center;
  gap: 8px;
}
.category-header .link { font-size: 0.9rem; font-weight: normal; }

.category-card .deck-info h3 { font-size: 1.1rem; }

.deck-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 14px 16px;
  margin-bottom: 12px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  flex-wrap: wrap;
}
.deck-info h3 { margin: 0 0 4px; }
.deck-actions { display: flex; align-items: center; gap: 8px; flex-wrap: wrap; }
.deck-option {
  display: flex;
  align-items: center;
  gap: 6px;
  font-size: 0.85rem;
  color: var(--muted);
  cursor: pointer;
}

.manage-section {
  margin-top: 24px;
  padding-top: 16px;
  border-top: 1px solid var(--border);
}

.card-row {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 10px;
  border: 1px solid var(--border);
  border-radius: 8px;
  margin-bottom: 8px;
  background: var(--surface);
  flex-wrap: wrap;
}
.card-row-front { font-weight: 600; }
.card-row-back { flex: 1; }

.badge {
  display: inline-block;
  font-size: 0.7rem;
  padding: 2px 8px;
  border-radius: 999px;
  background: var(--primary);
  color: #fff;
  opacity: 0.85;
}

/* Study */
.study-stage {
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 260px;
  perspective: 1000px;
}

.flash-card {
  width: 100%;
  max-width: min(600px, 92vw);
  min-height: 200px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 20px;
  box-shadow: 0 10px 30px rgba(0,0,0,0.08);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  text-align: center;
  gap: 12px;
  padding: 24px;
  touch-action: pan-y;
  user-select: none;
  cursor: grab;
  position: relative;
}
.flash-card.dragging { cursor: grabbing; }
.flash-card .card-main { font-size: clamp(1.8rem, 1rem + 4vw, 3.4rem); font-weight: 700; }
.flash-card .card-main.small { font-size: clamp(1.3rem, 0.8rem + 3vw, 2.6rem); font-weight: 600; }
.flash-card .card-example { color: var(--muted); margin-top: 8px; }
.flash-card .card-example.large { color: var(--text); font-size: clamp(1.1rem, 0.7rem + 2vw, 1.8rem); line-height: 1.6; margin-top: 0; }
.flash-card .card-note { color: var(--muted); font-size: 0.8rem; margin-top: 8px; }
.flash-card .tap-hint { font-size: 0.8rem; color: var(--muted); }

.study-controls {
  display: flex;
  flex-direction: column;
  gap: 12px;
  margin-top: 20px;
}

.answer-buttons {
  display: flex;
  gap: 12px;
}

.answer-block {
  flex: 1;
  min-height: 92px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.4rem;
  font-weight: 700;
  line-height: 1.4;
  border-radius: 16px;
}

.delete-card-btn {
  align-self: center;
  color: var(--danger);
  font-size: 0.85rem;
  padding: 8px 16px;
}

.face-options {
  display: flex;
  gap: 16px;
  flex-wrap: wrap;
  padding: 10px 12px;
  margin-bottom: 12px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 10px;
  font-size: 0.9rem;
}
.face-options label { display: flex; align-items: center; gap: 6px; cursor: pointer; }

.drive-bar {
  margin-top: 16px;
  padding-top: 16px;
  border-top: 1px dashed var(--border);
}
.drive-bar button.active {
  background: var(--danger);
  border-color: var(--danger);
}
.drive-buttons {
  display: flex;
  gap: 8px;
}
.drive-buttons .primary.wide { flex: 1; }
.shadow-option {
  margin-top: 10px;
  justify-content: center;
}

/* Forms */
.settings-form, .card-form {
  display: flex;
  flex-direction: column;
  gap: 14px;
}
.settings-form label, .card-form label {
  display: flex;
  flex-direction: column;
  gap: 6px;
  font-size: 0.9rem;
  color: var(--muted);
}
.settings-form input, .settings-form select,
.card-form input, .card-form select, .card-form textarea {
  font: inherit;
  padding: 8px 10px;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: var(--bg);
  color: var(--text);
}
.example-row { display: flex; gap: 8px; align-items: flex-start; }
.example-row textarea { flex: 1; }

.auth-box {
  max-width: 360px;
  margin: 60px auto;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 16px;
  padding: 28px;
}
.auth-box form {
  display: flex;
  flex-direction: column;
  gap: 14px;
}
.auth-box label {
  display: flex;
  flex-direction: column;
  gap: 6px;
  font-size: 0.9rem;
  color: var(--muted);
}
.auth-box input {
  font: inherit;
  padding: 10px;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: var(--bg);
  color: var(--text);
}

.two-col {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 14px;
}
@media (max-width: 480px) {
  .two-col { grid-template-columns: 1fr; }
}

/* Modal */
.modal {
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,0.4);
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 16px;
  z-index: 100;
}
.modal-content {
  background: var(--surface);
  border-radius: 16px;
  padding: 20px;
  max-width: 480px;
  width: 100%;
  max-height: 90vh;
  overflow-y: auto;
}
.modal-actions {
  display: flex;
  gap: 10px;
  margin-top: 16px;
}

@media (max-width: 480px) {
  button.wide { width: 100%; }
  .answer-block { font-size: 1.1rem; }
}

.toast {
  position: fixed;
  left: 50%;
  bottom: 24px;
  transform: translateX(-50%);
  background: var(--text);
  color: var(--bg);
  padding: 10px 18px;
  border-radius: 999px;
  font-size: 0.85rem;
  box-shadow: 0 6px 20px rgba(0,0,0,0.25);
  z-index: 200;
  transition: opacity 0.2s ease;
}