:root {
  color-scheme: dark;
  --bg: #101413;
  --surface: #171d1b;
  --surface-raised: #1d2522;
  --surface-soft: #202a26;
  --text: #eef2eb;
  --text-muted: #aab5ad;
  --text-faint: #7e8a83;
  --line: #2a3731;
  --line-strong: #3b4b42;
  --accent: #c7ee72;
  --accent-strong: #a8d452;
  --accent-ink: #17200f;
  --danger: #ff9d9d;
  --focus: #e0ff9f;
  --shadow: 0 18px 45px rgba(0, 0, 0, 0.24);
  --radius-card: 18px;
  --radius-control: 12px;
  font-family: ui-sans-serif, -apple-system, BlinkMacSystemFont, "Segoe UI", "Hiragino Kaku Gothic ProN", Meiryo, sans-serif;
}

html[data-theme="light"] {
  color-scheme: light;
  --bg: #eef1ed;
  --surface: #ffffff;
  --surface-raised: #f7faf5;
  --surface-soft: #e9efe7;
  --text: #17201b;
  --text-muted: #5b675e;
  --text-faint: #778279;
  --line: #d7e0d8;
  --line-strong: #b8c7b9;
  --accent: #547d17;
  --accent-strong: #41620f;
  --accent-ink: #f8fff0;
  --danger: #a73939;
  --focus: #355a09;
  --shadow: 0 18px 45px rgba(33, 53, 37, 0.12);
}

* {
  box-sizing: border-box;
}

html {
  min-width: 320px;
  background: var(--bg);
}

body {
  min-width: 320px;
  min-height: 100dvh;
  margin: 0;
  background: var(--bg);
  color: var(--text);
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
}

button {
  font: inherit;
}

button:focus-visible {
  outline: 3px solid var(--focus);
  outline-offset: 3px;
}

button:disabled {
  cursor: not-allowed;
  opacity: 0.42;
}

.app-shell {
  width: min(100%, 820px);
  min-height: 100dvh;
  margin: 0 auto;
  padding-bottom: calc(24px + env(safe-area-inset-bottom));
}

.topbar {
  position: sticky;
  top: 0;
  z-index: 5;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  min-height: 72px;
  padding: 14px 22px;
  border-bottom: 1px solid var(--line);
  background: color-mix(in srgb, var(--bg) 94%, transparent);
  backdrop-filter: blur(14px);
}

.brand-block {
  display: grid;
  gap: 1px;
}

.brand-kicker,
.section-kicker,
.face-label,
.empty-label {
  color: var(--accent);
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.12em;
}

.brand-kicker,
.section-kicker,
.empty-label {
  text-transform: uppercase;
}

.brand-block h1 {
  margin: 0;
  font-size: 1.22rem;
  letter-spacing: -0.025em;
}

.top-actions {
  display: flex;
  align-items: center;
  gap: 8px;
}

.button {
  display: inline-flex;
  min-height: 44px;
  align-items: center;
  justify-content: center;
  gap: 8px;
  border: 1px solid transparent;
  border-radius: var(--radius-control);
  padding: 10px 14px;
  color: var(--text);
  cursor: pointer;
  font-size: 0.9rem;
  font-weight: 700;
  line-height: 1.2;
  text-decoration: none;
  transition: background-color 140ms ease, border-color 140ms ease, color 140ms ease, transform 100ms ease;
}

.button:active {
  transform: scale(0.98);
}

.button-primary {
  border-color: var(--accent);
  background: var(--accent);
  color: var(--accent-ink);
}

.button-primary:hover {
  border-color: var(--accent-strong);
  background: var(--accent-strong);
}

.button-outline {
  border-color: var(--line-strong);
  background: transparent;
  color: var(--text);
}

.button-outline:hover,
.button-outline.is-favorite {
  border-color: var(--accent);
  color: var(--accent);
}

.button-quiet {
  min-height: 38px;
  padding: 8px 10px;
  border-color: transparent;
  background: transparent;
  color: var(--text-muted);
}

.button-quiet:hover,
.button-quiet[aria-pressed="true"] {
  color: var(--accent);
  background: var(--surface-soft);
}

.count-badge {
  display: inline-grid;
  min-width: 22px;
  height: 22px;
  place-items: center;
  border-radius: 999px;
  background: var(--surface-soft);
  color: var(--text-muted);
  font-size: 0.75rem;
  font-variant-numeric: tabular-nums;
}

.content {
  display: grid;
  gap: 18px;
  padding: 26px 22px 0;
}

.deck-panel,
.progress-panel {
  border: 1px solid var(--line);
  border-radius: var(--radius-card);
  background: var(--surface);
}

.deck-panel {
  padding: 20px;
}

.section-heading,
.progress-copy,
.deck-tools,
.card-meta,
.card-actions,
.card-nav {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
}

.section-heading {
  align-items: flex-start;
}

.section-heading h2,
.empty-state h2 {
  margin: 5px 0 0;
  font-size: 1.2rem;
  letter-spacing: -0.025em;
}

.deck-summary {
  color: var(--text-muted);
  font-size: 0.85rem;
  font-variant-numeric: tabular-nums;
  white-space: nowrap;
}

.deck-tabs {
  display: flex;
  gap: 8px;
  margin-top: 18px;
  overflow-x: auto;
  padding-bottom: 3px;
  scrollbar-width: thin;
}

.deck-tab {
  flex: 0 0 auto;
  min-height: 42px;
  padding: 9px 13px;
  border: 1px solid var(--line);
  border-radius: var(--radius-control);
  background: var(--surface-raised);
  color: var(--text-muted);
  cursor: pointer;
  font-size: 0.86rem;
  font-weight: 700;
  white-space: nowrap;
}

.deck-tab:hover,
.deck-tab[aria-selected="true"] {
  border-color: var(--accent);
  background: var(--surface-soft);
  color: var(--accent);
}

.deck-tools {
  justify-content: flex-start;
  margin-top: 16px;
}

.tool-note,
.keyboard-note {
  color: var(--text-faint);
  font-size: 0.82rem;
}

.progress-panel {
  padding: 15px 18px 17px;
}

.progress-copy {
  color: var(--text-muted);
  font-size: 0.8rem;
  font-variant-numeric: tabular-nums;
}

.progress-track {
  height: 5px;
  margin-top: 10px;
  overflow: hidden;
  border-radius: 999px;
  background: var(--surface-soft);
}

.progress-track span {
  display: block;
  width: 0;
  height: 100%;
  border-radius: inherit;
  background: var(--accent);
}

.flashcard {
  overflow: hidden;
  border: 1px solid var(--line-strong);
  border-radius: var(--radius-card);
  background: var(--surface-raised);
  box-shadow: var(--shadow);
}

.card-face {
  display: flex;
  min-height: 480px;
  flex-direction: column;
  padding: 22px;
}

.card-back {
  background: var(--surface);
}

.card-meta {
  color: var(--text-muted);
  font-size: 0.82rem;
  font-variant-numeric: tabular-nums;
}

.card-meta span:last-child {
  color: var(--text);
  font-weight: 700;
}

.question-block {
  display: grid;
  gap: 14px;
  margin: 38px 0 26px;
}

.face-label {
  font-size: 0.72rem;
}

.question-text {
  max-width: 70ch;
  margin: 0;
  font-size: clamp(1.06rem, 2.3vw, 1.28rem);
  font-weight: 600;
  line-height: 1.75;
  white-space: pre-wrap;
}

.choice-list {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 10px;
  margin-top: auto;
}

.choice-button {
  display: flex;
  min-height: 58px;
  align-items: center;
  gap: 10px;
  padding: 10px 12px;
  border: 1px solid var(--line);
  border-radius: var(--radius-control);
  background: var(--surface);
  color: var(--text);
  cursor: pointer;
  text-align: left;
  transition: background-color 140ms ease, border-color 140ms ease, color 140ms ease, transform 100ms ease;
}

.choice-button:hover,
.choice-button[aria-pressed="true"] {
  border-color: var(--accent);
  background: var(--surface-soft);
}

.choice-button:active {
  transform: scale(0.99);
}

.choice-number {
  display: inline-grid;
  width: 28px;
  height: 28px;
  flex: 0 0 28px;
  place-items: center;
  border: 1px solid var(--line-strong);
  border-radius: 9px;
  color: var(--text-muted);
  font-size: 0.8rem;
  font-variant-numeric: tabular-nums;
}

.choice-button[aria-pressed="true"] .choice-number {
  border-color: var(--accent);
  background: var(--accent);
  color: var(--accent-ink);
}

.choice-text {
  overflow-wrap: anywhere;
  font-size: 0.95rem;
}

.card-actions {
  justify-content: flex-start;
  flex-wrap: wrap;
  margin-top: 24px;
}

.card-actions .button-primary {
  min-width: 190px;
}

.favorite-button {
  min-width: 148px;
}

.answer-block {
  display: grid;
  gap: 10px;
  margin: 36px 0 18px;
  padding: 18px 20px;
  border-left: 3px solid var(--accent);
  background: var(--surface-soft);
}

.answer-word {
  margin: 0;
  color: var(--accent);
  font-size: clamp(1.55rem, 5vw, 2.15rem);
  font-weight: 800;
  letter-spacing: -0.035em;
  overflow-wrap: anywhere;
}

.answer-position {
  margin: 0;
  color: var(--text-muted);
  font-size: 0.85rem;
}

.guess-result {
  min-height: 26px;
  margin-bottom: 18px;
  color: var(--text-muted);
  font-size: 0.9rem;
  font-weight: 700;
}

.guess-result.is-correct {
  color: var(--accent);
}

.guess-result.is-wrong {
  color: var(--danger);
}

.explanation-block {
  display: grid;
  gap: 12px;
  margin-top: 4px;
}

.explanation-content {
  display: grid;
  gap: 10px;
  color: var(--text-muted);
  font-size: 0.94rem;
  line-height: 1.75;
}

.explanation-content p {
  margin: 0;
}

.card-nav {
  justify-content: stretch;
}

.nav-button {
  flex: 1;
  min-height: 50px;
}

.empty-state {
  display: grid;
  justify-items: start;
  gap: 8px;
  padding: 34px 24px;
  border: 1px solid var(--line);
  border-radius: var(--radius-card);
  background: var(--surface);
}

.empty-state p {
  max-width: 40ch;
  margin: 0 0 12px;
  color: var(--text-muted);
}

.keyboard-note {
  margin: 0;
  text-align: center;
}

.app-footer {
  padding: 30px 22px 0;
  color: var(--text-faint);
  font-size: 0.76rem;
  text-align: center;
}

/* Concentration view: use the available viewport for the question itself. */
.focus-mode {
  overflow-x: hidden;
}

.focus-mode .app-shell {
  width: 100%;
  max-width: none;
  padding-bottom: 0;
}

.focus-mode .content {
  gap: 0;
  padding: 0;
}

.focus-mode .deck-panel,
.focus-mode .progress-panel,
.focus-mode .keyboard-note,
.focus-mode .app-footer {
  display: none;
}

.focus-mode #card-stage {
  min-height: calc(100dvh - 72px);
}

.focus-mode .flashcard {
  min-height: calc(100dvh - 72px);
  border-right: 0;
  border-left: 0;
  border-radius: 0;
  box-shadow: none;
}

.focus-mode .card-face {
  min-height: calc(100dvh - 72px);
  padding: clamp(24px, 5vw, 56px) clamp(18px, 6vw, 72px) calc(24px + env(safe-area-inset-bottom));
}

.focus-mode .question-block {
  margin: clamp(32px, 8vh, 76px) 0 32px;
}

.focus-mode .question-text {
  max-width: 78ch;
  font-size: clamp(1.24rem, 3.2vw, 1.82rem);
  line-height: 1.75;
}

.focus-mode .choice-list,
.focus-mode .card-actions,
.focus-mode .card-back .answer-block,
.focus-mode .card-back .explanation-block,
.focus-mode .card-back .guess-result {
  width: min(100%, 860px);
}

.focus-mode .choice-list {
  gap: 12px;
}

.focus-mode .choice-button {
  min-height: 68px;
  padding: 14px 16px;
}

.focus-mode .choice-text {
  font-size: 1.05rem;
}

.focus-mode .card-actions {
  margin-top: 30px;
}

.focus-mode .card-actions .button-primary {
  min-width: 230px;
}

.focus-mode .card-back .answer-block {
  margin-top: clamp(30px, 7vh, 64px);
}

.focus-mode .explanation-content {
  font-size: 1.02rem;
  line-height: 1.85;
}

.focus-mode .card-nav {
  position: sticky;
  bottom: 0;
  z-index: 4;
  width: min(100%, 980px);
  margin: 0 auto;
  padding: 12px clamp(18px, 6vw, 72px) calc(12px + env(safe-area-inset-bottom));
  border-top: 1px solid var(--line);
  background: color-mix(in srgb, var(--bg) 94%, transparent);
  backdrop-filter: blur(14px);
}

[hidden] {
  display: none !important;
}

@media (max-width: 600px) {
  .topbar {
    min-height: 64px;
    padding: 12px 16px;
  }

  .top-actions {
    gap: 3px;
  }

  .top-actions .button {
    font-size: 0.78rem;
  }

  .content {
    gap: 14px;
    padding: 18px 14px 0;
  }

  .deck-panel {
    padding: 17px;
  }

  .card-face {
    min-height: 500px;
    padding: 18px;
  }

  .question-block {
    margin-top: 32px;
  }

  .choice-list {
    grid-template-columns: 1fr;
  }

  .card-actions {
    align-items: stretch;
  }

  .card-actions .button {
    flex: 1 1 100%;
  }

  .card-actions .button-primary {
    min-width: 0;
  }

  .keyboard-note {
    padding: 0 8px;
  }

  .focus-mode .topbar {
    padding: 12px 10px;
  }

  .focus-mode .top-actions {
    gap: 0;
  }

  .focus-mode .top-actions .button {
    padding-right: 6px;
    padding-left: 6px;
  }

  .focus-mode .card-face {
    min-height: calc(100dvh - 64px);
    padding: 20px 16px calc(18px + env(safe-area-inset-bottom));
  }

  .focus-mode .question-block {
    margin: 32px 0 24px;
  }

  .focus-mode .question-text {
    font-size: clamp(1.12rem, 5.3vw, 1.42rem);
  }

  .focus-mode .choice-button {
    min-height: 62px;
    padding: 12px 13px;
  }

  .focus-mode .card-actions {
    margin-top: 22px;
  }

  .focus-mode .card-actions .button {
    flex: 1 1 auto;
  }

  .focus-mode .card-actions .button-primary {
    min-width: 0;
  }

  .focus-mode .explanation-content {
    font-size: 0.98rem;
  }

  .focus-mode .card-nav {
    padding-right: 16px;
    padding-left: 16px;
  }
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    scroll-behavior: auto !important;
    transition-duration: 0.01ms !important;
    animation-duration: 0.01ms !important;
  }
}