:root {
  --bg: #101410;
  --raise: #1b2420;
  --sunken: #0c100e;
  --line: #314038;
  --text: #f3f0e4;
  --muted: #b7c0b4;
  --brass: #e0b15a;
  --brass-ink: #23190a;
  --moss: #9dccae;
  --clay: #e7a196;
  --sans: "Segoe UI", "Avenir Next", "Helvetica Neue", Helvetica, Arial, sans-serif;
  --serif: Georgia, "Iowan Old Style", "Palatino Linotype", Palatino, "Times New Roman", serif;
  color-scheme: dark;
}

* { box-sizing: border-box; }

[hidden] { display: none !important; }

html { font-size: 16px; }

body {
  margin: 0;
  min-height: 100vh;
  font-family: var(--sans);
  color: var(--text);
  background:
    radial-gradient(900px 420px at 0% -10%, rgba(224, 177, 90, 0.16), transparent 55%),
    radial-gradient(720px 480px at 100% 0%, rgba(157, 204, 174, 0.08), transparent 46%),
    var(--bg);
  line-height: 1.5;
}

button, input { font: inherit; color: inherit; }

button { cursor: pointer; }

:focus-visible {
  outline: 2px solid var(--brass);
  outline-offset: 2px;
}

.wrap {
  width: min(880px, 100%);
  margin: 0 auto;
  padding: 20px 16px 48px;
}

header {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  gap: 16px 24px;
  align-items: flex-end;
  padding-bottom: 18px;
  border-bottom: 1px solid var(--line);
}

.eyebrow {
  margin: 0 0 2px;
  color: var(--brass);
  font-size: 0.75rem;
  letter-spacing: 0.14em;
  text-transform: uppercase;
}

h1 {
  margin: 0;
  font-family: var(--serif);
  font-size: 1.85rem;
  font-weight: 600;
  letter-spacing: -0.02em;
}

#brand {
  background: none;
  border: 0;
  padding: 0;
  color: inherit;
  font: inherit;
  letter-spacing: inherit;
}

.stats {
  display: flex;
  flex-wrap: wrap;
  gap: 10px 18px;
}

.stat-group {
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  gap: 8px 12px;
}

.group-label {
  color: var(--muted);
  font-size: 0.72rem;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

.stat {
  display: inline-flex;
  align-items: baseline;
  gap: 5px;
}

.stat-value {
  font-variant-numeric: tabular-nums;
  font-weight: 600;
  font-size: 1.05rem;
}

.stat-value.hot { color: var(--brass); }

.stat-label {
  color: var(--muted);
  font-size: 0.82rem;
}

.hero { margin: 28px 0 18px; }

h2 {
  margin: 0;
  font-family: var(--serif);
  font-size: 1.7rem;
  font-weight: 600;
  letter-spacing: -0.02em;
}

.lede {
  margin: 8px 0 0;
  max-width: 40rem;
  color: var(--muted);
  font-size: 1.05rem;
}

.topic-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 12px;
}

.topic {
  display: flex;
  flex-direction: column;
  align-items: flex-start;
  gap: 4px;
  text-align: left;
  background: var(--raise);
  border: 1px solid var(--line);
  border-radius: 18px;
  padding: 16px 18px 18px;
  box-shadow: 0 12px 30px rgba(0, 0, 0, 0.18);
}

.topic:hover { border-color: var(--brass); }

.topic-name {
  font-family: var(--serif);
  font-size: 1.35rem;
}

.topic-count {
  color: var(--brass);
  font-size: 0.82rem;
  letter-spacing: 0.04em;
}

.topic-blurb { color: var(--muted); }

.card {
  margin-top: 22px;
  background: var(--raise);
  border: 1px solid var(--line);
  border-radius: 20px;
  padding: 18px 16px 20px;
  box-shadow: 0 16px 40px rgba(0, 0, 0, 0.22);
}

.meta-row {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  align-items: center;
  gap: 12px;
}

.meta-side {
  display: flex;
  align-items: center;
  gap: 10px;
}

.timer {
  font-variant-numeric: tabular-nums;
  font-weight: 600;
  font-size: 1.15rem;
  color: var(--brass);
  letter-spacing: 0.02em;
}

.progress {
  margin: 4px 0 14px;
  color: var(--muted);
  font-size: 0.92rem;
}

.pill {
  border: 1px solid var(--line);
  border-radius: 999px;
  padding: 3px 10px;
  color: var(--muted);
  font-size: 0.75rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.pill[data-level="hard"] {
  color: var(--clay);
  border-color: rgba(231, 161, 150, 0.65);
}

.prompt {
  margin: 0 0 18px;
  font-size: 1.28rem;
  line-height: 1.45;
}

.math-display {
  margin: 10px 0;
  overflow-x: auto;
  text-align: center;
}

.choices {
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.choice {
  display: flex;
  align-items: center;
  gap: 12px;
  width: 100%;
  min-height: 52px;
  padding: 10px 14px;
  text-align: left;
  background: var(--sunken);
  border: 1px solid var(--line);
  border-radius: 14px;
}

.choice-key {
  flex: 0 0 auto;
  width: 1.7rem;
  height: 1.7rem;
  display: grid;
  place-items: center;
  border: 1px solid var(--line);
  border-radius: 999px;
  color: var(--muted);
  font-size: 0.85rem;
}

.choice-body {
  flex: 1;
  min-width: 0;
  font-size: 1.05rem;
  overflow-wrap: break-word;
}

.choice-tag {
  margin-left: auto;
  font-size: 0.72rem;
  font-weight: 600;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.choice.is-selected {
  border-color: var(--brass);
  box-shadow: inset 0 0 0 1px var(--brass);
}

.choice.is-correct {
  border-color: var(--moss);
  background: rgba(157, 204, 174, 0.14);
  box-shadow: inset 4px 0 0 var(--moss);
}

.choice.is-wrong {
  border-color: var(--clay);
  background: rgba(231, 161, 150, 0.14);
  box-shadow: inset 4px 0 0 var(--clay);
}

.choice.is-correct .choice-tag { color: var(--moss); }

.choice.is-wrong .choice-tag { color: var(--clay); }

.choice:disabled {
  opacity: 1;
  color: var(--text);
  -webkit-text-fill-color: var(--text);
  cursor: default;
}

#check-btn { margin-top: 12px; }

.primary, .ghost {
  min-height: 48px;
  border-radius: 999px;
  padding: 10px 18px;
}

.primary {
  background: var(--brass);
  color: var(--brass-ink);
  border: 0;
  font-weight: 600;
}

.primary:disabled, .ghost:disabled {
  opacity: 0.55;
  cursor: default;
}

.ghost {
  background: transparent;
  border: 1px solid var(--line);
}

.format-note, .form-error {
  margin: 8px 0 0;
  font-size: 0.86rem;
}

.format-note { color: var(--muted); }

.form-error { color: var(--clay); }

.tool-row {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-top: 16px;
}

.hint {
  margin: 12px 0 0;
  padding: 12px 14px;
  background: rgba(224, 177, 90, 0.08);
  border-left: 3px solid var(--brass);
  border-radius: 8px;
}

.learn {
  margin-top: 14px;
  padding: 14px 14px 12px;
  background: var(--sunken);
  border: 1px solid var(--line);
  border-radius: 14px;
}

.learn h3 {
  margin: 12px 0 6px;
  font-size: 0.78rem;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--brass);
}

.learn h3:first-child { margin-top: 0; }

.learn p { margin: 0; }

.formula { overflow-x: auto; }

.learn-link-row { margin-top: 12px !important; }

.learn a {
  color: var(--brass);
  overflow-wrap: anywhere;
}

.result {
  margin-top: 16px;
  padding: 14px;
  border-radius: 14px;
  border: 1px solid var(--line);
}

.result.correct {
  background: rgba(157, 204, 174, 0.1);
  border-color: rgba(157, 204, 174, 0.45);
}

.result.incorrect {
  background: rgba(231, 161, 150, 0.1);
  border-color: rgba(231, 161, 150, 0.45);
}

.result-title {
  margin: 0 0 6px;
  font-family: var(--serif);
  font-size: 1.45rem;
}

.result.correct .result-title { color: var(--moss); }

.result.incorrect .result-title { color: var(--clay); }

.result-line { margin: 0 0 6px; color: var(--muted); }

.result-line strong { color: var(--text); font-weight: 600; }

.official { font-size: 1.2rem; }

.explanation {
  margin-top: 12px;
  padding: 10px 12px;
  border-radius: 8px;
  border-left: 3px solid var(--clay);
  background: rgba(231, 161, 150, 0.12);
}

.explanation.is-light {
  border-left-color: var(--line);
  background: transparent;
  color: var(--muted);
}

.explanation-label {
  margin: 0 0 4px;
  font-size: 0.78rem;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--brass);
}

.explanation.is-light .explanation-label { color: var(--muted); }

.explanation-body { line-height: 1.45; }

#next-btn { margin-top: 12px; }

.done .eyebrow { margin-bottom: 6px; }

.time-result {
  margin: 14px 0 0;
  font-family: var(--serif);
  font-size: 1.65rem;
  line-height: 1.3;
  color: var(--brass);
  font-variant-numeric: tabular-nums;
}

.card.is-challenge {
  box-shadow: inset 0 3px 0 var(--brass), 0 16px 40px rgba(0, 0, 0, 0.22);
}

.challenge-card {
  margin-top: 16px;
  background: var(--raise);
  border: 1px solid var(--line);
  border-radius: 18px;
  padding: 16px 18px 18px;
  box-shadow: 0 12px 30px rgba(0, 0, 0, 0.18);
}

.challenge-card h2 { font-size: 1.45rem; }

.challenge-best {
  margin: 10px 0 14px;
  color: var(--brass);
  font-variant-numeric: tabular-nums;
}

footer {
  margin-top: 28px;
  color: var(--muted);
  font-size: 0.85rem;
}

footer p { margin: 0; }

footer .credit {
  margin-top: 6px;
  font-size: 0.75rem;
}

footer .credit a {
  color: inherit;
}

@media (min-width: 700px) {
  .wrap { padding: 32px 24px 64px; }
  .topic-grid { grid-template-columns: 1fr 1fr; }
  .card { padding: 22px 22px 24px; }
  .prompt { font-size: 1.4rem; }
}

@media (max-width: 520px) {
  .primary, .ghost { width: 100%; }
  h1 { font-size: 1.6rem; }
}

@media (prefers-reduced-motion: reduce) {
  * { scroll-behavior: auto !important; }
}