:root {
  --bg: #0f1115;
  --card-bg: #1a1d24;
  --text: #e8eaed;
  --text-dim: #9aa0a8;
  --accent: #6c8cff;
  --green: #2e7d4f;
  --green-bg: #163d27;
  --red: #b3454a;
  --red-bg: #3d1a1c;
  --border: #2a2e37;
  --radius: 14px;
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  background: var(--bg);
  color: var(--text);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  -webkit-text-size-adjust: 100%;
}

.app {
  min-height: 100vh;
  min-height: 100dvh;
  display: flex;
  flex-direction: column;
  max-width: 560px;
  margin: 0 auto;
  padding: env(safe-area-inset-top) env(safe-area-inset-right) env(safe-area-inset-bottom) env(safe-area-inset-left);
}

.topbar {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  padding: 18px 20px 8px;
}

.deck-title {
  font-size: 15px;
  font-weight: 600;
  color: var(--text-dim);
  letter-spacing: 0.02em;
  text-transform: uppercase;
}

.stats {
  font-size: 13px;
  color: var(--text-dim);
  font-variant-numeric: tabular-nums;
}

.card-wrap {
  flex: 1;
  display: flex;
  flex-direction: column;
  padding: 12px 20px 20px;
  gap: 16px;
}

.deck-switcher {
  display: flex;
  gap: 8px;
  padding: 0 20px 12px;
}

.deck-pill {
  flex: 1;
  padding: 9px 10px;
  border-radius: 999px;
  border: 1px solid var(--border);
  background: var(--card-bg);
  color: var(--text-dim);
  font-size: 13px;
  font-weight: 600;
  cursor: pointer;
  -webkit-tap-highlight-color: transparent;
  transition: background 0.15s ease, border-color 0.15s ease, color 0.15s ease;
}

.deck-pill.active {
  background: var(--accent);
  border-color: var(--accent);
  color: #0f1115;
}

.question-card {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 28px 22px;
  min-height: 96px;
  display: flex;
  align-items: center;
}

.question {
  margin: 0;
  font-size: 19px;
  line-height: 1.45;
  font-weight: 500;
}

.options {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.option-card {
  display: block;
  width: 100%;
  text-align: left;
  background: var(--card-bg);
  border: 1px solid var(--border);
  color: var(--text);
  border-radius: var(--radius);
  padding: 0;
  font-size: 16px;
  line-height: 1.4;
  cursor: pointer;
  transition: background 0.15s ease, border-color 0.15s ease, transform 0.1s ease;
  -webkit-tap-highlight-color: transparent;
  perspective: 600px;
  overflow: hidden;
}

.option-card:active {
  transform: scale(0.98);
}

.option-card:hover {
  border-color: var(--accent);
}

.option-card.correct {
  background: var(--green-bg);
  border-color: var(--green);
  color: #d3f5e0;
}

.option-card.incorrect {
  background: var(--red-bg);
  border-color: var(--red);
  color: #f7d6d7;
}

.option-inner {
  padding: 16px 18px;
  transition: transform 0.16s ease-in;
  transform: rotateX(0deg);
  backface-visibility: hidden;
}

.option-inner.flip-mid {
  transform: rotateX(90deg);
  transition-timing-function: ease-in;
}

.option-letter {
  display: inline-block;
  width: 22px;
  font-weight: 700;
  color: var(--text-dim);
}

.option-card.correct .option-letter,
.option-card.incorrect .option-letter {
  color: inherit;
}

.tag {
  display: block;
  font-weight: 700;
  margin-bottom: 4px;
  text-transform: uppercase;
  font-size: 11px;
  letter-spacing: 0.04em;
  opacity: 0.85;
}

.option-explanation {
  font-size: 14px;
}

.feedback {
  display: flex;
  flex-direction: column;
  gap: 14px;
  animation: fadeIn 0.2s ease;
}

@keyframes fadeIn {
  from { opacity: 0; transform: translateY(4px); }
  to { opacity: 1; transform: translateY(0); }
}

.next-btn {
  width: 100%;
  padding: 15px;
  border-radius: var(--radius);
  border: none;
  background: var(--accent);
  color: #0f1115;
  font-size: 16px;
  font-weight: 700;
  cursor: pointer;
  -webkit-tap-highlight-color: transparent;
}

.next-btn:active {
  opacity: 0.85;
}

.footer {
  text-align: center;
  padding: 8px 20px 22px;
}

.reset-link {
  background: none;
  border: none;
  color: var(--text-dim);
  font-size: 12px;
  cursor: pointer;
  padding: 6px;
  text-decoration: underline;
  opacity: 0.6;
}

.reset-link:active {
  opacity: 1;
}

@media (max-width: 380px) {
  .question { font-size: 17px; }
  .option-card { font-size: 15px; }
  .option-inner { padding: 14px 16px; }
}