:root {
  color-scheme: dark;
  --bg: #0c1116;
  --bg-raise: #151c24;
  --line: #2a3846;
  --text: #e8eef4;
  --muted: #93a3b3;
  --teal: #6ee0c4;
  --teal-dim: #17352e;
  --rose: #ff6b81;
  --rose-dim: #3a2229;
  --good: #7ddea8;
  --good-dim: #163226;
  --bad: #ff8b98;
  --bad-dim: #3a2228;
  --blue: #6aa4d6;
  --shadow: 0 18px 50px rgba(0, 0, 0, 0.35);
  --sans: "Segoe UI", "Avenir Next", "Trebuchet MS", sans-serif;
}

* { box-sizing: border-box; }

html, body { margin: 0; min-height: 100%; }

body {
  font-family: var(--sans);
  background:
    radial-gradient(900px 420px at 10% -10%, rgba(255, 107, 129, 0.14), transparent 55%),
    radial-gradient(800px 480px at 110% 0%, rgba(110, 224, 196, 0.1), transparent 50%),
    var(--bg);
  color: var(--text);
  line-height: 1.5;
}

.page {
  width: min(820px, calc(100% - 32px));
  margin: 0 auto;
  padding: 28px 0 64px;
}

.topbar { margin-bottom: 22px; }

.brand {
  display: flex;
  align-items: center;
  gap: 14px;
}

.logo-heart {
  width: 42px;
  height: 42px;
  fill: var(--rose);
  flex: none;
  transform-origin: center;
  animation: beat 1.3s ease-in-out infinite;
}

.brand-kicker,
.kicker {
  margin: 0;
  color: var(--teal);
  font-size: 0.78rem;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  font-weight: 700;
}

.brand-title {
  margin: 2px 0 0;
  font-size: 1.05rem;
  font-weight: 650;
}

.panel {
  background: var(--bg-raise);
  border: 1px solid var(--line);
  border-radius: 20px;
  box-shadow: var(--shadow);
  padding: 28px 28px 24px;
}

h1 {
  margin: 8px 0 10px;
  font-size: clamp(2rem, 4vw, 2.7rem);
  line-height: 1.1;
  letter-spacing: -0.03em;
}

.lede, .note, .hint, .footer-note {
  color: var(--muted);
}

.lede { margin: 0 0 18px; font-size: 1.05rem; }

.eq {
  margin: 0 0 22px;
  padding: 14px 16px;
  border-left: 3px solid var(--rose);
  background: #121920;
  border-radius: 0 12px 12px 0;
}

.eq strong { display: block; color: var(--text); font-size: 1.08rem; margin-top: 2px; }

.modes {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
  margin-bottom: 16px;
}

.mode {
  display: flex;
  gap: 10px;
  align-items: flex-start;
  border: 1px solid var(--line);
  border-radius: 14px;
  padding: 12px 14px;
  cursor: pointer;
  background: #10171e;
}

.mode:has(input:checked) {
  border-color: var(--teal);
  background: var(--teal-dim);
}

.mode input { margin-top: 4px; accent-color: var(--teal); }

.mode strong { display: block; color: var(--text); }

.hint { display: block; font-size: 0.92rem; }

.field { margin: 0 0 18px; }

.field span {
  display: block;
  margin-bottom: 6px;
  font-size: 0.92rem;
}

.field input {
  width: 100%;
  border: 1px solid var(--line);
  background: #0e151c;
  color: var(--text);
  border-radius: 12px;
  padding: 12px 14px;
  font: inherit;
}

.field input:focus-visible,
.choice:focus-visible,
.primary:focus-visible,
.ghost:focus-visible,
.review summary:focus-visible {
  outline: 2px solid var(--teal);
  outline-offset: 2px;
}

.actions, .nav {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  align-items: center;
}

.primary, .ghost {
  font: inherit;
  border-radius: 999px;
  padding: 12px 18px;
  cursor: pointer;
  border: 1px solid transparent;
}

.primary {
  background: var(--rose);
  color: #2a0d13;
  font-weight: 750;
}

.primary:disabled,
.ghost:disabled {
  opacity: 0.45;
  cursor: not-allowed;
}

.ghost {
  background: transparent;
  color: var(--text);
  border-color: var(--line);
}

.footer-note { margin: 18px 0 0; font-size: 0.86rem; }

.meta {
  display: flex;
  justify-content: space-between;
  gap: 12px;
  align-items: baseline;
  margin-bottom: 8px;
  color: var(--muted);
  font-size: 0.92rem;
}

.topic {
  color: var(--teal);
  font-weight: 700;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  font-size: 0.78rem;
}

.progress {
  height: 8px;
  background: #0e151c;
  border-radius: 99px;
  overflow: hidden;
  margin-bottom: 18px;
}

.progress-bar {
  height: 100%;
  background: linear-gradient(90deg, var(--rose), var(--teal));
  width: 0;
}

.prompt {
  margin: 0 0 16px;
  font-size: 1.28rem;
  line-height: 1.35;
  letter-spacing: -0.02em;
}

.prompt:focus { outline: none; }

.diagram {
  margin: 0 0 16px;
  background: #0e151c;
  border: 1px solid var(--line);
  border-radius: 16px;
  padding: 12px 12px 8px;
}

.diagram svg {
  display: block;
  width: auto;
  max-width: 100%;
  height: 250px;
  margin: 0 auto;
}

.diagram figcaption {
  color: var(--muted);
  font-size: 0.9rem;
  margin-top: 4px;
}

.choices {
  display: grid;
  gap: 10px;
  margin-bottom: 16px;
}

.choice {
  display: flex;
  gap: 12px;
  align-items: flex-start;
  text-align: left;
  width: 100%;
  font: inherit;
  color: var(--text);
  background: #10171e;
  border: 1px solid var(--line);
  border-radius: 14px;
  padding: 12px 14px;
  cursor: pointer;
}

.choice:hover:not(:disabled) { border-color: #4c6274; }

.choice .key {
  flex: none;
  width: 1.7rem;
  height: 1.7rem;
  border-radius: 999px;
  display: grid;
  place-items: center;
  background: #243140;
  font-size: 0.85rem;
  font-weight: 750;
}

.choice.selected {
  border-color: var(--teal);
  background: #13262a;
}

.choice.correct {
  border-color: var(--good);
  background: var(--good-dim);
}

.choice.wrong {
  border-color: var(--bad);
  background: var(--bad-dim);
}

.choice:disabled { cursor: default; }

.feedback {
  border-radius: 14px;
  padding: 12px 14px;
  margin-bottom: 16px;
}

.feedback.good { background: var(--good-dim); color: #d9f7e6; }
.feedback.bad { background: var(--bad-dim); color: #ffd5db; }
.feedback strong { display: block; margin-bottom: 4px; }

.score-wrap {
  display: flex;
  gap: 18px;
  align-items: flex-start;
  margin-bottom: 8px;
}

.score-num {
  flex: none;
  white-space: nowrap;
  font-size: 3rem;
  line-height: 1;
  letter-spacing: -0.04em;
  color: var(--teal);
}

.score-num span { color: var(--muted); font-size: 1.4rem; }

.score-name { margin: 0; font-size: 1.7rem; }

.review { display: grid; gap: 10px; margin-top: 18px; }

.review details {
  border: 1px solid var(--line);
  border-radius: 14px;
  padding: 10px 14px;
  background: #10171e;
}

.review summary { cursor: pointer; font-weight: 650; }
.review .miss summary { color: var(--bad); }
.review .hit summary { color: var(--good); }
.review p { margin: 8px 0; }
.review .answer-line { color: var(--muted); }

.path {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  margin: 14px 0 0;
}

.path span {
  background: #10171e;
  border: 1px solid var(--line);
  border-radius: 999px;
  padding: 4px 10px;
  font-size: 0.86rem;
}

.noscript {
  width: min(820px, calc(100% - 32px));
  margin: 20px auto;
}

@media (max-width: 680px) {
  .modes { grid-template-columns: 1fr; }
  .panel { padding: 22px 16px 18px; }
  .prompt { font-size: 1.15rem; }
  .score-wrap { flex-direction: column; }
  .diagram svg { height: 220px; }
}

@media (prefers-reduced-motion: reduce) {
  .logo-heart { animation: none; }
}

@keyframes beat {
  0%, 100% { transform: scale(1); }
  18% { transform: scale(1.14); }
  32% { transform: scale(1); }
  48% { transform: scale(1.08); }
}