:root {
  /* light theme (default) */
  --bg: #f7f8fa;
  --bg-elev: #ffffff;
  --bg-elev-2: #f1f3f7;
  --border: #e3e6ec;
  --border-strong: #c9cfd9;
  --text: #1a1f2b;
  --text-dim: #5a6473;
  --text-faint: #8a93a3;
  --accent: #3b5bff;
  --accent-2: #2a48e0;
  --accent-on: #ffffff;
  --success: #15a05a;
  --success-bg: rgba(21, 160, 90, 0.10);
  --success-border: rgba(21, 160, 90, 0.35);
  --error: #d23a3a;
  --error-bg: rgba(210, 58, 58, 0.08);
  --error-border: rgba(210, 58, 58, 0.35);
  --warn: #c98a09;
  --easy: #15a05a;
  --medium: #c98a09;
  --hard: #d23a3a;
  --shadow: 0 4px 24px rgba(20, 28, 50, 0.08);
  --shadow-strong: 0 8px 32px rgba(20, 28, 50, 0.12);
  --radius: 14px;
  --bg-glow-1: rgba(59, 91, 255, 0.06);
  --bg-glow-2: rgba(21, 160, 90, 0.04);
}

[data-theme="dark"] {
  --bg: #0e1116;
  --bg-elev: #161b22;
  --bg-elev-2: #1d2330;
  --border: #262d3a;
  --border-strong: #364154;
  --text: #e6edf3;
  --text-dim: #9aa6b2;
  --text-faint: #6b7785;
  --accent: #7c9eff;
  --accent-2: #5b7fff;
  --accent-on: #0e1116;
  --success: #4ade80;
  --success-bg: rgba(74, 222, 128, 0.12);
  --success-border: rgba(74, 222, 128, 0.25);
  --error: #f87171;
  --error-bg: rgba(248, 113, 113, 0.12);
  --error-border: rgba(248, 113, 113, 0.28);
  --warn: #fbbf24;
  --easy: #4ade80;
  --medium: #fbbf24;
  --hard: #f87171;
  --shadow: 0 8px 32px rgba(0, 0, 0, 0.32);
  --shadow-strong: 0 12px 40px rgba(0, 0, 0, 0.5);
  --bg-glow-1: rgba(124, 158, 255, 0.10);
  --bg-glow-2: rgba(74, 222, 128, 0.06);
}

* { box-sizing: border-box; }
html, body { margin: 0; padding: 0; }
body {
  background: radial-gradient(1200px 600px at 80% -20%, var(--bg-glow-1), transparent 60%),
              radial-gradient(900px 500px at -10% 110%, var(--bg-glow-2), transparent 60%),
              var(--bg);
  color: var(--text);
  font-family: 'Inter', -apple-system, system-ui, sans-serif;
  font-size: 15px;
  line-height: 1.55;
  min-height: 100vh;
  -webkit-font-smoothing: antialiased;
  transition: background-color 200ms ease, color 200ms ease;
}

#app {
  max-width: 760px;
  margin: 0 auto;
  padding: 56px 24px 80px;
}

.hidden { display: none !important; }

/* floating toolbar (theme + settings) */
.toolbar {
  position: fixed;
  top: 20px;
  right: 20px;
  display: flex;
  gap: 8px;
  z-index: 10;
}
.toolbar-btn {
  width: 38px; height: 38px;
  display: grid;
  place-items: center;
  background: var(--bg-elev);
  border: 1px solid var(--border);
  border-radius: 10px;
  color: var(--text-dim);
  cursor: pointer;
  transition: color 140ms ease, border-color 140ms ease, background 140ms ease, transform 140ms ease;
  box-shadow: var(--shadow);
  padding: 0;
}
.toolbar-btn:hover { color: var(--accent); border-color: var(--border-strong); transform: translateY(-1px); }

#theme-toggle .icon-sun { display: none; }
#theme-toggle .icon-moon { display: block; }
[data-theme="dark"] #theme-toggle .icon-sun { display: block; }
[data-theme="dark"] #theme-toggle .icon-moon { display: none; }

/* Quit button: shown only during an active session.
   Hidden on the settings/start screen (nothing to quit) and on results (results screen has its own actions). */
#quit-toggle { display: none; }
body[data-screen="session-screen"] #quit-toggle { display: inline-flex; }

.quit-btn {
  width: auto;
  padding: 0 14px;
  gap: 6px;
  font-size: 13.5px;
  font-weight: 600;
  font-family: inherit;
}
.quit-btn span { line-height: 1; }
.quit-btn:hover {
  color: var(--error);
  border-color: color-mix(in srgb, var(--error) 40%, var(--border));
}
.screen { animation: fade 220ms ease; }
@keyframes fade { from { opacity: 0; transform: translateY(4px); } to { opacity: 1; transform: none; } }

/* ---------- start screen ---------- */

.brand {
  display: flex;
  gap: 18px;
  align-items: center;
  margin-bottom: 36px;
}
.logo {
  width: 56px; height: 56px;
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  color: var(--accent-on);
  border-radius: 14px;
  display: grid;
  place-items: center;
  font-weight: 700;
  letter-spacing: 0.5px;
  font-size: 17px;
  box-shadow: 0 6px 20px rgba(124, 158, 255, 0.35);
}
.brand-text h1 {
  margin: 0;
  font-size: 26px;
  font-weight: 700;
  letter-spacing: -0.01em;
}
.subtitle {
  margin: 4px 0 0;
  color: var(--text-dim);
  font-size: 14.5px;
}

.config-card {
  background: var(--bg-elev);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 28px;
  box-shadow: var(--shadow);
}
.config-card h2 {
  margin: 0 0 22px;
  font-size: 17px;
  font-weight: 600;
}

.config-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 22px 28px;
}
.field-full { grid-column: 1 / -1; }
.field { display: flex; flex-direction: column; gap: 10px; }
.field-label {
  font-size: 12px;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-faint);
  font-weight: 600;
}

select {
  appearance: none;
  background: var(--bg-elev-2);
  color: var(--text);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 11px 14px;
  font-size: 14.5px;
  font-family: inherit;
  cursor: pointer;
  background-image: url("data:image/svg+xml;utf8,<svg xmlns='http://www.w3.org/2000/svg' width='12' height='12' viewBox='0 0 12 12'><path fill='currentColor' d='M6 8L2 4h8z'/></svg>");
  color: var(--text);
  background-repeat: no-repeat;
  background-position: right 12px center;
  padding-right: 36px;
}
select:focus { outline: 2px solid var(--accent); outline-offset: 1px; }

.chip-row { display: flex; gap: 8px; flex-wrap: wrap; }
.chip {
  background: var(--bg-elev-2);
  color: var(--text-dim);
  border: 1px solid var(--border);
  border-radius: 999px;
  padding: 8px 16px;
  font-size: 13.5px;
  font-weight: 500;
  cursor: pointer;
  font-family: inherit;
  transition: all 140ms ease;
}
.chip:hover { color: var(--text); border-color: var(--border-strong); }
/* "selected" filter — visually subordinate to the primary CTA */
.chip.active {
  background: color-mix(in srgb, var(--accent) 14%, var(--bg-elev));
  color: var(--accent);
  border-color: color-mix(in srgb, var(--accent) 38%, transparent);
  font-weight: 600;
}

.config-footer {
  display: flex;
  flex-direction: column;
  gap: 14px;
  margin-top: 28px;
  padding-top: 22px;
  border-top: 1px solid var(--border);
}
.pool-info {
  color: var(--text-dim);
  font-size: 13.5px;
  text-align: center;
}
.pool-info #pool-count {
  color: var(--text);
  font-weight: 600;
}

#start-btn {
  width: 100%;
  padding: 18px 24px;
  font-size: 16px;
  font-weight: 700;
  letter-spacing: 0.01em;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 10px;
  border-radius: 12px;
  box-shadow: 0 8px 22px color-mix(in srgb, var(--accent) 38%, transparent);
}
#start-btn:hover { box-shadow: 0 10px 28px color-mix(in srgb, var(--accent) 50%, transparent); }
#start-btn .arrow {
  display: inline-block;
  transition: transform 160ms ease;
  font-size: 18px;
}
#start-btn:hover .arrow { transform: translateX(4px); }

/* ---------- buttons ---------- */

.btn-primary {
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  color: var(--accent-on);
  border: none;
  border-radius: 10px;
  padding: 11px 20px;
  font-size: 14.5px;
  font-weight: 600;
  font-family: inherit;
  cursor: pointer;
  box-shadow: 0 4px 14px color-mix(in srgb, var(--accent) 36%, transparent);
  transition: transform 120ms ease, box-shadow 120ms ease, opacity 120ms ease;
}
.btn-primary:hover:not(:disabled) { transform: translateY(-1px); box-shadow: 0 6px 18px color-mix(in srgb, var(--accent) 50%, transparent); }
.btn-primary:active:not(:disabled) { transform: translateY(0); }
.btn-primary:disabled { opacity: 0.45; cursor: not-allowed; box-shadow: none; }

.btn-ghost {
  background: transparent;
  color: var(--text-dim);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 9px 16px;
  font-size: 14px;
  font-weight: 500;
  font-family: inherit;
  cursor: pointer;
  transition: all 140ms ease;
}
.btn-ghost:hover { color: var(--text); border-color: var(--border-strong); }

/* ---------- session screen ---------- */

.session-header {
  display: flex;
  align-items: center;
  gap: 18px;
  margin-bottom: 24px;
  padding-right: 96px; /* leave room for the floating toolbar on small screens */
}
.progress { flex: 1; }
.progress-meta {
  font-size: 13px;
  color: var(--text-dim);
  margin-bottom: 8px;
  font-variant-numeric: tabular-nums;
}
.progress-meta .dot { margin: 0 8px; opacity: 0.5; }
#q-index, #score-display { color: var(--text); font-weight: 600; }
.progress-bar {
  height: 4px;
  background: var(--bg-elev-2);
  border-radius: 999px;
  overflow: hidden;
}
.progress-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--accent), var(--accent-2));
  width: 0%;
  transition: width 300ms ease;
}

.qcard {
  background: var(--bg-elev);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 32px;
  box-shadow: var(--shadow);
}
.qcard-meta { display: flex; gap: 10px; margin-bottom: 18px; flex-wrap: wrap; }
.tag {
  display: inline-flex;
  align-items: baseline;
  gap: 6px;
  font-size: 12.5px;
  font-weight: 600;
  padding: 5px 12px;
  border-radius: 999px;
  letter-spacing: 0.01em;
  line-height: 1.4;
}
.tag-label {
  font-size: 12.5px;
  font-weight: 500;
  opacity: 0.7;
}
.tag-label::after { content: ':'; }
.tag-value { font-weight: 600; }

.tag-topic {
  background: color-mix(in srgb, var(--accent) 12%, transparent);
  color: var(--accent);
  border: 1px solid color-mix(in srgb, var(--accent) 32%, transparent);
}
/* Subtopic uses the same accent family as topic but a softer fill — they read as related. */
.tag-subtopic {
  background: color-mix(in srgb, var(--accent) 6%, transparent);
  color: var(--accent);
  border: 1px solid color-mix(in srgb, var(--accent) 22%, transparent);
}
.tag-difficulty .tag-value { text-transform: capitalize; }
.tag-difficulty.easy { background: color-mix(in srgb, var(--easy) 10%, transparent); color: var(--easy); border: 1px solid color-mix(in srgb, var(--easy) 30%, transparent); }
.tag-difficulty.medium { background: color-mix(in srgb, var(--medium) 12%, transparent); color: var(--medium); border: 1px solid color-mix(in srgb, var(--medium) 32%, transparent); }
.tag-difficulty.hard { background: color-mix(in srgb, var(--hard) 10%, transparent); color: var(--hard); border: 1px solid color-mix(in srgb, var(--hard) 30%, transparent); }

.question {
  font-size: 19px;
  font-weight: 600;
  line-height: 1.45;
  margin: 0 0 24px;
  letter-spacing: -0.005em;
}

.options { display: flex; flex-direction: column; gap: 10px; }
.option {
  display: flex;
  gap: 14px;
  align-items: flex-start;
  text-align: left;
  width: 100%;
  background: var(--bg-elev-2);
  border: 1px solid var(--border);
  color: var(--text);
  border-radius: 12px;
  padding: 14px 16px;
  font-size: 15px;
  font-family: inherit;
  cursor: pointer;
  transition: all 140ms ease;
}
.option:hover:not(:disabled) {
  border-color: var(--accent);
  background: color-mix(in srgb, var(--accent) 5%, var(--bg-elev-2));
}
.option:disabled { cursor: default; }
.option-key {
  font-family: 'JetBrains Mono', ui-monospace, monospace;
  font-size: 12.5px;
  font-weight: 600;
  width: 24px; height: 24px;
  display: grid;
  place-items: center;
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 6px;
  color: var(--text-dim);
  flex-shrink: 0;
  margin-top: 1px;
}
.option-text { flex: 1; }
.option-mark {
  margin-left: auto;
  font-size: 16px;
  font-weight: 700;
  flex-shrink: 0;
}

.option.correct {
  border-color: var(--success);
  background: var(--success-bg);
}
.option.correct .option-key {
  background: var(--success);
  color: var(--accent-on);
  border-color: var(--success);
}
.option.correct .option-mark { color: var(--success); }

.option.incorrect {
  border-color: var(--error);
  background: var(--error-bg);
}
.option.incorrect .option-key {
  background: var(--error);
  color: var(--accent-on);
  border-color: var(--error);
}
.option.incorrect .option-mark { color: var(--error); }

.option.muted { opacity: 0.55; }

.explanation {
  margin-top: 22px;
  padding: 16px 18px;
  background: var(--bg-elev-2);
  border-left: 3px solid var(--accent);
  border-radius: 8px;
}
.explanation-label {
  font-size: 11.5px;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--accent);
  font-weight: 700;
  margin-bottom: 6px;
}
.explanation p { margin: 0; color: var(--text); font-size: 14.5px; }

.qcard-footer {
  display: flex;
  justify-content: flex-end;
  margin-top: 22px;
}

/* ---------- results screen ---------- */

.results-card {
  background: var(--bg-elev);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 36px;
  box-shadow: var(--shadow);
  text-align: center;
}
.results-score {
  display: inline-flex;
  align-items: baseline;
  gap: 16px;
  padding: 22px 32px;
  background: var(--bg-elev-2);
  border-radius: 14px;
  margin-bottom: 22px;
}
.score-number {
  font-size: 44px;
  font-weight: 700;
  letter-spacing: -0.02em;
  font-variant-numeric: tabular-nums;
}
.score-divider { color: var(--text-faint); margin: 0 4px; font-weight: 400; }
.score-pct {
  font-size: 20px;
  font-weight: 600;
  color: var(--accent);
}
#results-headline {
  margin: 0 0 6px;
  font-size: 22px;
  font-weight: 700;
}
.results-sub {
  margin: 0 0 24px;
  color: var(--text-dim);
}
.results-actions {
  display: flex;
  justify-content: center;
  gap: 10px;
  margin-bottom: 28px;
}
.results-misses {
  text-align: left;
  border-top: 1px solid var(--border);
  padding-top: 22px;
}
.miss {
  background: var(--bg-elev-2);
  border-radius: 10px;
  padding: 16px;
  margin-bottom: 12px;
  font-size: 14px;
}
.miss-q { font-weight: 600; margin-bottom: 12px; line-height: 1.4; color: var(--text); }

.miss-answers {
  display: flex;
  flex-direction: column;
  gap: 8px;
  margin-bottom: 12px;
}
.miss-answer {
  display: grid;
  grid-template-columns: auto auto 1fr;
  align-items: center;
  gap: 10px;
  padding: 10px 12px;
  border-radius: 8px;
  border: 1px solid;
  font-size: 13.5px;
  line-height: 1.4;
}
.miss-answer-wrong {
  background: var(--error-bg);
  border-color: var(--error-border);
}
.miss-answer-right {
  background: var(--success-bg);
  border-color: var(--success-border);
}
.miss-answer-label {
  font-size: 10.5px;
  text-transform: uppercase;
  letter-spacing: 0.07em;
  font-weight: 700;
  white-space: nowrap;
}
.miss-answer-wrong .miss-answer-label { color: var(--error); }
.miss-answer-right .miss-answer-label { color: var(--success); }
.miss-answer-key {
  font-family: 'JetBrains Mono', ui-monospace, monospace;
  font-size: 11.5px;
  font-weight: 700;
  width: 22px; height: 22px;
  display: grid;
  place-items: center;
  border-radius: 5px;
  color: var(--accent-on);
}
.miss-answer-wrong .miss-answer-key { background: var(--error); }
.miss-answer-right .miss-answer-key { background: var(--success); }
.miss-answer-text {
  color: var(--text);
  font-weight: 500;
  min-width: 0;
  overflow-wrap: anywhere;
}

.miss-explanation {
  background: var(--bg-elev);
  border-left: 3px solid var(--accent);
  border-radius: 6px;
  padding: 10px 12px;
  font-size: 13px;
  color: var(--text-dim);
  margin-bottom: 10px;
  line-height: 1.5;
}
.miss-meta {
  color: var(--text-dim);
  font-size: 12px;
  font-weight: 500;
}
.miss-meta-label {
  color: var(--text-faint);
  font-weight: 600;
}

@media (max-width: 600px) {
  .config-grid { grid-template-columns: 1fr; gap: 18px; }
  .qcard, .config-card, .results-card { padding: 22px; }
  .question { font-size: 17.5px; }
}