:root {
  --bg: #f6f7f4;
  --card: #ffffff;
  --text: #17211a;
  --muted: #667169;
  --border: #dfe4df;
  --accent: #1d6b4f;
  --accent-soft: #e7f3ed;
  --correct: #17653f;
  --correct-soft: #e6f5ec;
  --incorrect: #9a3d32;
  --incorrect-soft: #faece9;
  --shadow: 0 14px 34px rgba(25, 40, 30, 0.08);
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
}

* { box-sizing: border-box; }
body { margin: 0; background: var(--bg); color: var(--text); }
button, input { font: inherit; }
button { cursor: pointer; }

.app-shell { width: min(100%, 720px); margin: 0 auto; padding: 24px 18px 56px; }
.screen { display: none; }
.screen.active { display: block; }
.hidden { display: none !important; }

.brand-row { display: flex; align-items: center; gap: 10px; margin: 8px 2px 34px; }
.brand-row.compact { margin-bottom: 22px; }
.brand-mark { width: 34px; height: 34px; border-radius: 11px; display: grid; place-items: center; background: var(--text); color: white; font-weight: 800; }
.brand-name { font-weight: 750; letter-spacing: -0.02em; }

.hero-card, .results-card, .question-card { background: var(--card); border: 1px solid var(--border); border-radius: 24px; box-shadow: var(--shadow); }
.hero-card, .results-card { padding: 28px 22px; }
.question-card { padding: 24px 20px; }

.eyebrow { margin: 0 0 10px; color: var(--accent); font-weight: 750; font-size: 0.92rem; }
h1 { margin: 0; font-size: clamp(2rem, 8vw, 3.8rem); line-height: 1.03; letter-spacing: -0.055em; }
.subcopy, .score-message { color: var(--muted); line-height: 1.55; margin: 18px 0 24px; }

.selector-button { width: 100%; display: flex; align-items: center; justify-content: space-between; gap: 14px; border: 1px solid var(--border); background: #fafbfa; border-radius: 16px; padding: 14px 16px; text-align: left; color: var(--text); }
.selector-button small, .chapter-option small { display: block; color: var(--muted); margin-bottom: 2px; }
.chevron { font-size: 1.35rem; }
.chapter-panel { border: 1px solid var(--border); border-top: 0; margin-top: -4px; padding: 14px; border-radius: 0 0 16px 16px; background: white; }
.chapter-option { display: flex; gap: 12px; align-items: flex-start; padding: 8px 2px; }
.chapter-option input { margin-top: 4px; }
.future-note { color: var(--muted); font-size: 0.84rem; line-height: 1.45; margin: 12px 2px 2px; }

.primary-button, .secondary-button { width: 100%; border-radius: 15px; padding: 15px 18px; font-weight: 750; }
.primary-button { border: 0; color: white; background: var(--accent); margin-top: 18px; }
.primary-button:disabled { opacity: 0.45; cursor: not-allowed; }
.secondary-button { border: 1px solid var(--border); background: white; color: var(--text); margin-top: 10px; }

.ad-slot { min-height: 84px; border: 1px dashed #cbd2cc; color: #879088; margin-top: 24px; border-radius: 16px; display: grid; place-items: center; font-size: 0.8rem; background: rgba(255,255,255,.45); }

.quiz-topbar { display: flex; gap: 14px; align-items: center; margin-bottom: 18px; }
.ghost-button { width: 40px; height: 40px; border: 0; background: transparent; color: var(--muted); font-size: 1.6rem; }
.ghost-button.back { width: auto; font-size: 0.95rem; font-weight: 700; padding: 8px 0; }
.progress-wrap { flex: 1; display: flex; align-items: center; gap: 12px; }
.progress-track { flex: 1; height: 9px; background: #e6e9e6; border-radius: 999px; overflow: hidden; }
.progress-fill { height: 100%; background: var(--accent); width: 10%; transition: width 240ms ease; }
#progress-label { color: var(--muted); font-size: 0.85rem; min-width: 44px; text-align: right; }

.question-meta { margin-bottom: 18px; }
.topic-pill { display: inline-flex; background: var(--accent-soft); color: var(--accent); padding: 7px 10px; border-radius: 999px; font-size: 0.78rem; font-weight: 750; }
.question-card h2 { font-size: clamp(1.35rem, 5vw, 2rem); line-height: 1.3; letter-spacing: -0.03em; margin: 0 0 20px; }
.answers { display: grid; gap: 11px; }
.answer-button { width: 100%; border: 1px solid var(--border); background: white; border-radius: 15px; padding: 15px; text-align: left; line-height: 1.4; color: var(--text); transition: 120ms ease; }
.answer-button:hover:not(:disabled) { border-color: #aeb7b0; transform: translateY(-1px); }
.answer-button.correct { border-color: var(--correct); background: var(--correct-soft); }
.answer-button.incorrect { border-color: var(--incorrect); background: var(--incorrect-soft); }
.answer-button.dimmed { opacity: 0.62; }
.answer-button:disabled { cursor: default; }

.feedback { margin-top: 20px; padding-top: 18px; border-top: 1px solid var(--border); }
.feedback-heading { display: flex; align-items: center; gap: 8px; }
.feedback-icon { width: 26px; height: 26px; border-radius: 50%; display: grid; place-items: center; font-weight: 800; }
.feedback.correct .feedback-icon { background: var(--correct-soft); color: var(--correct); }
.feedback.incorrect .feedback-icon { background: var(--incorrect-soft); color: var(--incorrect); }
.feedback p { color: var(--muted); line-height: 1.55; margin: 10px 0 0; }

.learning-reference {
  margin-top: 16px;
  padding: 14px 15px;
  border: 1px solid var(--border);
  border-radius: 14px;
  background: var(--surface);
  display: grid;
  gap: 4px;
}
.learning-reference-label {
  color: var(--muted);
  font-size: 0.75rem;
  font-weight: 750;
  text-transform: uppercase;
  letter-spacing: 0.04em;
}
.learning-reference strong {
  font-size: 0.9rem;
  line-height: 1.35;
}
.learning-reference #feedback-concept {
  color: var(--muted);
  font-size: 0.88rem;
  line-height: 1.4;
}


.results-card h1 { font-size: clamp(3rem, 13vw, 5rem); }
.result-section { margin-top: 26px; }
.result-section h3 { margin: 0 0 11px; font-size: 1rem; }
.topic-results { display: flex; flex-wrap: wrap; gap: 8px; }
.topic-chip { padding: 8px 10px; border: 1px solid var(--border); background: #fafbfa; border-radius: 999px; font-size: 0.84rem; }
.result-actions { margin-top: 28px; }

.review-topbar { margin-bottom: 12px; }
#review-title { font-size: clamp(2rem, 8vw, 3rem); margin-bottom: 24px; }
.review-list { display: grid; gap: 14px; }
.review-item { background: white; border: 1px solid var(--border); border-radius: 18px; padding: 18px; }
.review-item h3 { margin: 0 0 10px; font-size: 1rem; line-height: 1.4; }
.review-item p { margin: 6px 0; color: var(--muted); line-height: 1.5; }
.review-status { font-size: 0.78rem; font-weight: 800; text-transform: uppercase; letter-spacing: .04em; }
.review-status.correct { color: var(--correct); }
.review-status.incorrect { color: var(--incorrect); }

@media (min-width: 640px) {
  .app-shell { padding-top: 42px; }
  .hero-card, .results-card { padding: 38px 36px; }
  .question-card { padding: 34px 32px; }
}