:root {
  --bg: #f7f8fa;
  --surface: #ffffff;
  --text: #1f2933;
  --muted: #6b7684;
  --border: #dde2e8;
  --accent: #2f6fed;
  --right: #1f9d55;
  --wrong: #d64545;
  color-scheme: light dark;
}

/* OS設定によるダーク反映。data-theme="light" が明示されているときは無効化する
   (トグルボタンでの手動選択を優先するため)。 */
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #14181d;
    --surface: #1c2229;
    --text: #e6eaef;
    --muted: #9aa5b1;
    --border: #2c343d;
    --accent: #6aa1ff;
  }
}

/* トグルボタンでの手動選択(localStorage、theme.js)。OS設定より優先する。 */
:root[data-theme="dark"] {
  --bg: #14181d;
  --surface: #1c2229;
  --text: #e6eaef;
  --muted: #9aa5b1;
  --border: #2c343d;
  --accent: #6aa1ff;
}

* { box-sizing: border-box; }

/* hidden 属性は必ず効かせる。
   .actions や .choices の display:flex は作者スタイルなので、
   これがないとUAの [hidden]{display:none} に勝ってしまい、
   非表示にしたはずの要素が出たままになる。 */
[hidden] { display: none !important; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: system-ui, -apple-system, 'Hiragino Sans', 'Noto Sans JP', sans-serif;
  line-height: 1.7;
}

.site-header {
  position: sticky;
  top: 0;
  z-index: 10;
  background: color-mix(in srgb, var(--surface) 92%, transparent);
  backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--border);
}

.site-header-inner {
  max-width: 44rem;
  margin: 0 auto;
  padding: .85rem 1rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  flex-wrap: wrap;
}

.site-brand {
  display: flex;
  align-items: center;
  gap: .45rem;
  font-weight: 700;
  font-size: 1rem;
  color: var(--text);
  text-decoration: none;
}

.site-nav a {
  color: var(--muted);
  text-decoration: none;
  font-size: .85rem;
}
.site-nav a:hover { color: var(--accent); }

.theme-toggle {
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text);
  border-radius: 2rem;
  padding: .4rem 1rem;
  font-size: .8rem;
  cursor: pointer;
  white-space: nowrap;
}
.theme-toggle:hover { border-color: var(--accent); }

.site-footer {
  border-top: 1px solid var(--border);
  padding: 1.5rem 1rem;
  text-align: center;
  color: var(--muted);
  font-size: .8rem;
}
.site-footer .footer-notice {
  margin-top: .4rem;
  font-size: .75rem;
}

#app {
  max-width: 44rem;
  margin: 0 auto;
  padding: 1.5rem 1rem 4rem;
}

h1 { font-size: 1.35rem; margin: 0 0 1.25rem; }
h2 { font-size: 1rem; margin: 0 0 .5rem; color: var(--muted); }
h3 { font-size: .9rem; margin: 0 0 .25rem; }

fieldset {
  border: 1px solid var(--border);
  border-radius: .6rem;
  margin: 0 0 1rem;
  padding: .75rem 1rem 1rem;
  background: var(--surface);
}

legend {
  font-size: .85rem;
  color: var(--muted);
  padding: 0 .35rem;
}

.chips { display: flex; flex-wrap: wrap; gap: .5rem; }

.theme-groups { display: flex; flex-direction: column; gap: .35rem; }

.theme-group-heading {
  display: flex;
  align-items: center;
  gap: .4rem;
  font-size: .8rem;
  font-weight: 600;
  color: var(--muted);
  margin-top: .5rem;
  cursor: pointer;
  user-select: none;
}

.theme-group-heading:first-child { margin-top: 0; }

.chip {
  display: inline-flex;
  align-items: center;
  gap: .3rem;
  border: 1px solid var(--border);
  border-radius: 2rem;
  padding: .3rem .8rem;
  cursor: pointer;
  user-select: none;
  font-size: .9rem;
}

.chip:has(input:checked) {
  border-color: var(--accent);
  background: color-mix(in srgb, var(--accent) 12%, transparent);
}

input[type="number"] {
  width: 6rem;
  padding: .4rem .6rem;
  border: 1px solid var(--border);
  border-radius: .4rem;
  background: var(--bg);
  color: inherit;
  font: inherit;
}

.actions { display: flex; gap: .75rem; flex-wrap: wrap; margin-top: 1.25rem; }
.actions.column { flex-direction: column; align-items: stretch; }

button, .button {
  font: inherit;
  border-radius: .5rem;
  padding: .6rem 1.2rem;
  border: 1px solid var(--border);
  background: var(--surface);
  color: inherit;
  cursor: pointer;
  text-align: center;
}

button:disabled { opacity: .5; cursor: not-allowed; }
button.primary { background: var(--accent); border-color: var(--accent); color: #fff; }
button.danger { color: var(--wrong); border-color: var(--wrong); }
button.link {
  border: none;
  background: none;
  color: var(--accent);
  padding: 0 .4rem;
  font-size: .8rem;
}

.card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: .6rem;
  padding: 1.1rem 1.2rem;
  margin-bottom: 1rem;
}

.quiz-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  color: var(--muted);
  font-size: .85rem;
  margin-bottom: .75rem;
}

.quiz-header-actions { display: flex; align-items: center; gap: .25rem; }

/* 電卓はスクロール位置に関わらず操作できるよう画面下部に固定表示する。
   スマホの横持ちなど画面が低い環境では関数電卓モードの高さが画面をはみ出し、
   表示部やモード切替ボタンが操作不能になるため、高さの上限とスクロールを設ける。 */
.calculator {
  position: fixed;
  left: 50%;
  bottom: 1rem;
  transform: translateX(-50%);
  z-index: 20;
  width: min(19rem, calc(100% - 2rem));
  max-height: calc(100vh - 2rem);
  max-height: calc(100dvh - 2rem);
  overflow-y: auto;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: .6rem;
  box-shadow: 0 8px 24px rgba(0, 0, 0, .18);
  padding: .6rem;
}

.calculator-bar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  color: var(--muted);
  font-size: .8rem;
  margin-bottom: .4rem;
}

.calculator-bar-actions { display: flex; align-items: center; gap: .5rem; }

.calculator-mode-toggle {
  border: 1px solid var(--border);
  background: var(--bg);
  color: var(--text);
  border-radius: 1rem;
  padding: .15rem .6rem;
  font-size: .7rem;
  white-space: nowrap;
}
.calculator-mode-toggle[aria-pressed="true"] { border-color: var(--accent); color: var(--accent); }

.calculator-close {
  border: none;
  background: none;
  color: var(--muted);
  font-size: 1.1rem;
  line-height: 1;
  padding: 0 .3rem;
}

.calculator-expr {
  text-align: right;
  font-size: .8rem;
  color: var(--muted);
  font-variant-numeric: tabular-nums;
  padding: 0 .7rem;
  min-height: 1.1em;
  overflow-x: auto;
  white-space: nowrap;
}

.calculator-display {
  text-align: right;
  font-size: 1.4rem;
  font-variant-numeric: tabular-nums;
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: .4rem;
  padding: .5rem .7rem;
  margin-bottom: .5rem;
  overflow-x: auto;
  white-space: nowrap;
}

.calculator-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: .4rem;
}

.calculator-grid button { padding: .55rem 0; font-size: .95rem; }
.calculator-grid .calc-op { color: var(--accent); }
.calculator-grid .calc-equals { grid-column: span 2; }

.calculator-grid-sci { margin-bottom: .4rem; }
.calculator-grid-sci button { font-size: .85rem; }

.choices { display: flex; flex-direction: column; gap: .6rem; }
.choice { text-align: left; padding: .75rem 1rem; }
.choice.right { border-color: var(--right); background: color-mix(in srgb, var(--right) 14%, transparent); }
.choice.wrong { border-color: var(--wrong); background: color-mix(in srgb, var(--wrong) 14%, transparent); }

.answer { border-left: 3px solid var(--accent); }

.supplement {
  border-top: 1px solid var(--border);
  margin-top: .9rem;
  padding-top: .75rem;
}
.supplement h3 { color: var(--muted); font-weight: 600; }

.supplement-track { position: relative; }
.supplement-track.has-nav { padding: 0 2.6rem; }

.supplement-nav-btn {
  position: absolute;
  top: 50%;
  transform: translateY(-50%);
  width: 2.4rem;
  height: 2.4rem;
  padding: 0;
  border-radius: 50%;
  border: 1px solid var(--accent);
  background: var(--accent);
  color: #fff;
  font-size: 1.5rem;
  line-height: 1;
  display: flex;
  align-items: center;
  justify-content: center;
  box-shadow: 0 3px 10px color-mix(in srgb, var(--accent) 45%, transparent);
  cursor: pointer;
  transition: transform .12s ease, box-shadow .12s ease;
}
.supplement-nav-btn:hover:not(:disabled) { transform: translateY(-50%) scale(1.08); }
.supplement-nav-btn:active:not(:disabled) { transform: translateY(-50%) scale(.96); }
.supplement-nav-btn:disabled {
  background: var(--surface);
  border-color: var(--border);
  color: var(--muted);
  box-shadow: none;
  cursor: default;
  opacity: .5;
}
.supplement-nav-btn.prev { left: 0; }
.supplement-nav-btn.next { right: 0; }

.supplement-counter {
  display: block;
  text-align: center;
  margin-top: .6rem;
  color: var(--muted);
  font-size: .8rem;
}

.summary { color: var(--muted); font-size: .9rem; }
.note { color: var(--muted); font-size: .85rem; }

.error {
  background: color-mix(in srgb, var(--wrong) 12%, transparent);
  border: 1px solid var(--wrong);
  border-radius: .5rem;
  padding: .8rem 1rem;
  margin-top: 1rem;
}

/* 数式は横に溢れうるので、行内でスクロールさせる */
.katex-display { overflow-x: auto; overflow-y: hidden; padding: .2rem 0; }