:root {
  color-scheme: light dark;
  --bg: #0d1117;
  --panel: rgba(255, 255, 255, 0.06);
  --surface: rgba(17, 24, 39, 0.85);
  --text: #e6edf5;
  --text-muted: #8da0b6;
  --accent: #ff8b3d;
  --accent-soft: #ffb94f;
  --font-base: 'Noto Sans JP', system-ui, -apple-system, BlinkMacSystemFont, sans-serif;
  --font-japanese: 'Noto Sans JP', 'Hiragino Kaku Gothic Pro', sans-serif;
  font-family: var(--font-base);
}

* {
  box-sizing: border-box;
}

body {
  min-height: 100vh;
  margin: 0;
  background: radial-gradient(circle at top, rgba(255, 139, 61, 0.25), transparent 45%),
    #030712;
  color: var(--text);
  display: flex;
  justify-content: center;
  padding: 2rem 1rem;
}

.quiz-shell {
  width: min(960px, 100%);
  display: flex;
  flex-direction: column;
  gap: 1.5rem;
}

.hero h1 {
  margin: 0.25rem 0;
  font-size: clamp(2.25rem, 3vw, 3rem);
  letter-spacing: -0.02em;
}

.hero .eyebrow {
  text-transform: uppercase;
  letter-spacing: 0.4em;
  font-size: 0.75rem;
  color: var(--accent-soft);
}

.hero .lede {
  max-width: 56ch;
  line-height: 1.6;
  color: var(--text-muted);
}

.controls {
  display: flex;
  gap: 0.75rem;
  align-items: center;
  flex-wrap: wrap;
}

.mode-toggle {
  display: inline-flex;
  border: 1px solid rgba(255, 255, 255, 0.15);
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.02);
  padding: 0.25rem;
}

.mode-button {
  border: none;
  background: transparent;
  color: var(--text-muted);
  padding: 0.45rem 1.2rem;
  border-radius: 999px;
  cursor: pointer;
  font-weight: 600;
  transition: color 0.2s ease, background 0.2s ease;
}

.mode-button.active {
  background: linear-gradient(135deg, var(--accent), var(--accent-soft));
  color: #0b0b0b;
}

.ghost-button {
  border: 1px solid rgba(255, 255, 255, 0.35);
  background: transparent;
  border-radius: 999px;
  padding: 0.45rem 1.5rem;
  color: var(--text);
  cursor: pointer;
  font-weight: 600;
}

.ghost-button.mini {
  padding: 0.35rem 1rem;
  font-size: 0.85rem;
}

.flash-side-toggle {
  display: inline-flex;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.02);
  gap: 0.35rem;
  padding: 0.25rem;
}

.flash-side-toggle .ghost-button.mini.active {
  background: linear-gradient(135deg, var(--accent), var(--accent-soft));
  color: #0b0b0b;
  border-color: transparent;
}

.chapter-panel {
  padding: 1rem 1.25rem;
  border-radius: 18px;
  background: var(--panel);
  border: 1px solid rgba(255, 255, 255, 0.12);
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
}

.chapter-panel__header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.75rem;
  flex-wrap: wrap;
}

.chapter-actions {
  display: inline-flex;
  gap: 0.5rem;
}

.chapter-panel__title {
  margin: 0;
  font-size: 0.85rem;
  letter-spacing: 0.3em;
  text-transform: uppercase;
  color: var(--text-muted);
}

.chapter-chips {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.chapter-chip {
  border: 1px solid rgba(255, 255, 255, 0.3);
  background: rgba(255, 255, 255, 0.03);
  border-radius: 999px;
  padding: 0.35rem 1rem;
  font-size: 0.85rem;
  color: var(--text);
  cursor: pointer;
  transition: border 0.2s ease, background 0.2s ease;
}

.chapter-chip.active {
  border-color: var(--accent-soft);
  background: linear-gradient(120deg, rgba(255, 139, 61, 0.4), rgba(255, 139, 61, 0.18));
}

.chapter-note {
  margin: 0;
  font-size: 0.92rem;
  color: var(--text-muted);
}

.mode-help {
  padding: 1rem 1.25rem;
  border-radius: 18px;
  background: var(--panel);
  border: 1px solid rgba(255, 255, 255, 0.12);
  font-size: 0.95rem;
  color: var(--text-muted);
}

.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 1rem;
}

.card,
.write-card {
  position: relative;
  border-radius: 18px;
  min-height: 200px;
  background: rgba(255, 255, 255, 0.02);
  border: 1px solid rgba(255, 255, 255, 0.08);
  box-shadow: 0 10px 25px rgba(0, 0, 0, 0.35);
  overflow: hidden;
}

.card {
  perspective: 1200px;
}

.card-inner {
  position: relative;
  width: 100%;
  height: 100%;
  text-align: center;
  transition: transform 0.5s ease;
  transform-style: preserve-3d;
}

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

.card-face {
  position: absolute;
  inset: 0;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 1.25rem;
  backface-visibility: hidden;
}

.card-front {
  background: linear-gradient(140deg, rgba(255, 255, 255, 0.02), rgba(255, 255, 255, 0.1));
}

.card-back {
  background: rgba(255, 255, 255, 0.05);
  transform: rotateY(180deg);
  color: var(--text-muted);
}

.card .japanese {
  font-size: clamp(1.5rem, 2.5vw, 2.2rem);
  font-family: var(--font-japanese);
}

.card .english {
  font-size: 1rem;
  text-align: center;
}

.write-card {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
  padding: 1.25rem;
  position: relative;
}

.write-card .english {
  font-size: 1.15rem;
}

.write-card input {
  border: 1px solid rgba(255, 255, 255, 0.3);
  border-radius: 12px;
  padding: 0.65rem 0.9rem;
  font-size: 1rem;
  background: rgba(255, 255, 255, 0.04);
  color: var(--text);
}

.write-card input:focus {
  outline: 2px solid var(--accent);
}

.write-card .status {
  min-height: 1.2rem;
  font-weight: 600;
  font-size: 0.9rem;
}

.write-card .status.success {
  color: #7efc6a;
}

.write-card .status.error {
  color: #ff7b7b;
}

.tip-area {
  position: absolute;
  bottom: 1rem;
  right: 1rem;
  display: flex;
  flex-direction: column;
  align-items: flex-end;
  gap: 0.25rem;
}

.tip-mark {
  border: 1px solid rgba(255, 255, 255, 0.4);
  border-radius: 50%;
  width: 32px;
  height: 32px;
  background: rgba(255, 255, 255, 0.08);
  color: var(--text);
  font-weight: 600;
  cursor: pointer;
  display: grid;
  place-items: center;
  padding: 0;
}

.tip-text {
  font-size: 0.75rem;
  color: rgba(255, 255, 255, 0.9);
  text-align: right;
  max-width: 130px;
  opacity: 0;
  transition: opacity 0.2s ease;
  pointer-events: none;
  line-height: 1.2;
}

.tip-text.visible {
  opacity: 1;
}

@media (max-width: 600px) {
  body {
    padding: 1.5rem 1rem;
  }

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