:root {
  color-scheme: dark;
  --bg: #07111f;
  --panel: rgba(10, 24, 41, 0.94);
  --panel-2: rgba(255, 255, 255, 0.06);
  --text: #e9f1ff;
  --muted: #94a3b8;
  --accent: #8b5cf6;
  --accent-2: #22d3ee;
  --good: #34d399;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
  background: linear-gradient(135deg, var(--bg), #111827);
  color: var(--text);
  min-height: 100vh;
}

button {
  border: none;
  border-radius: 999px;
  padding: 0.75rem 1rem;
  font-size: 0.95rem;
  cursor: pointer;
  background: var(--panel-2);
  color: var(--text);
  transition: transform 0.2s ease, background 0.2s ease;
}

button:hover {
  transform: translateY(-1px);
  background: rgba(255, 255, 255, 0.12);
}

.app-shell {
  max-width: 1100px;
  margin: 0 auto;
  padding: 2rem 1rem 3rem;
}

.hero {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  align-items: center;
  padding: 1.25rem 1.5rem;
  background: linear-gradient(90deg, rgba(139, 92, 246, 0.25), rgba(34, 211, 238, 0.16));
  border: 1px solid rgba(255, 255, 255, 0.08);
  border-radius: 24px;
}

.eyebrow {
  text-transform: uppercase;
  letter-spacing: 0.2em;
  color: var(--accent-2);
  font-size: 0.8rem;
  margin: 0 0 0.3rem;
}

h1 {
  margin: 0;
  font-size: clamp(1.8rem, 4vw, 2.6rem);
}

.subtitle {
  max-width: 700px;
  color: var(--muted);
  line-height: 1.6;
  margin: 0.6rem 0 0;
}

.hero-badge {
  padding: 0.8rem 1rem;
  background: var(--panel);
  border: 1px solid rgba(255, 255, 255, 0.08);
  border-radius: 16px;
  color: var(--accent-2);
  white-space: nowrap;
}

.toolbar {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 1rem;
  margin: 1.2rem 0;
}

.stat-card {
  background: var(--panel);
  border: 1px solid rgba(255, 255, 255, 0.08);
  border-radius: 18px;
  padding: 1rem 1.1rem;
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.label {
  color: var(--muted);
  font-size: 0.9rem;
}

.content-grid {
  display: grid;
  grid-template-columns: 2fr 1fr;
  gap: 1rem;
}

.card-section,
.info-panel {
  background: var(--panel);
  border: 1px solid rgba(255, 255, 255, 0.08);
  border-radius: 24px;
  padding: 1.2rem;
}

.card-nav {
  display: flex;
  gap: 0.7rem;
  justify-content: center;
  margin-bottom: 1rem;
}

.flashcard {
  position: relative;
  min-height: 320px;
  perspective: 1200px;
  margin-bottom: 1rem;
}

.card-face {
  position: absolute;
  inset: 0;
  border-radius: 22px;
  padding: 1.2rem;
  background: linear-gradient(135deg, rgba(139, 92, 246, 0.2), rgba(34, 211, 238, 0.16));
  border: 1px solid rgba(255, 255, 255, 0.1);
  backface-visibility: hidden;
  transition: transform 0.6s ease;
  display: flex;
  flex-direction: column;
  justify-content: center;
  gap: 0.7rem;
}

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

.flashcard.flipped .back {
  transform: rotateY(0deg);
}

.front {
  transform: rotateY(0deg);
}

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

.card-tag {
  display: inline-block;
  width: fit-content;
  padding: 0.35rem 0.65rem;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.12);
  color: var(--accent-2);
  font-size: 0.85rem;
}

.card-hint,
.card-source,
.status {
  color: var(--muted);
}

.card-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.7rem;
}

.info-panel h3 {
  margin-top: 0;
}

.info-panel ul {
  list-style: none;
  padding: 0;
  margin: 0 0 1rem;
  display: grid;
  gap: 0.6rem;
}

.info-panel li {
  padding: 0.7rem 0.8rem;
  border-radius: 12px;
  background: rgba(255, 255, 255, 0.05);
  color: var(--text);
}

.favorite-list li {
  display: flex;
  justify-content: space-between;
  align-items: center;
}

@media (max-width: 860px) {
  .content-grid {
    grid-template-columns: 1fr;
  }

  .toolbar {
    grid-template-columns: 1fr;
  }

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