/* USABO AI — vanilla CSS, no framework */

:root {
  --bg: #f7f6f3;
  --surface: #ffffff;
  --border: #e0ddd6;
  --text: #26241f;
  --text-muted: #6b6858;
  --accent: #2f5d50;
  --accent-dark: #234840;
  --accent-soft: #e7efec;
  --correct: #2e7d32;
  --correct-soft: #e8f5e9;
  --incorrect: #c62828;
  --incorrect-soft: #fdecea;
  --partial: #b8860b;
  --partial-soft: #fdf3dc;
  --radius: 10px;
  --shadow: 0 1px 3px rgba(0,0,0,0.06), 0 1px 2px rgba(0,0,0,0.04);
  font-size: 16px;
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  background: var(--bg);
  color: var(--text);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif;
  line-height: 1.55;
}

h1, h2, h3, h4 {
  font-family: Georgia, "Times New Roman", serif;
  font-weight: 600;
  color: var(--text);
  margin: 0 0 0.5em;
}

p { margin: 0 0 1em; }

button {
  font-family: inherit;
  cursor: pointer;
}

/* Header */
.site-header {
  background: var(--accent);
  color: #fff;
  padding: 1.25rem 1.5rem;
}
.header-inner {
  max-width: 900px;
  margin: 0 auto;
}
.brand {
  color: #fff;
  font-size: 1.6rem;
  margin-bottom: 0.15em;
}
.tagline {
  color: #d9e8e2;
  margin: 0;
  font-size: 0.95rem;
}

/* Chapter nav */
.chapter-nav {
  max-width: 900px;
  margin: 1.25rem auto 0;
  padding: 0 1.5rem;
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
}
.chapter-btn {
  border: 1px solid var(--border);
  background: var(--surface);
  border-radius: var(--radius);
  padding: 0.55rem 0.9rem;
  font-size: 0.9rem;
  color: var(--text);
  display: flex;
  align-items: center;
  gap: 0.5rem;
  box-shadow: var(--shadow);
}
.chapter-btn.active {
  border-color: var(--accent);
  background: var(--accent-soft);
  color: var(--accent-dark);
  font-weight: 600;
}
.chapter-progress-dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--border);
  flex: none;
}
.chapter-progress-dot.full { background: var(--correct); }
.chapter-progress-dot.partial { background: var(--partial); }

/* Layer nav */
.layer-nav {
  max-width: 900px;
  margin: 1rem auto 0;
  padding: 0 1.5rem;
  display: flex;
  gap: 0.25rem;
  border-bottom: 1px solid var(--border);
}
.layer-btn {
  border: none;
  background: none;
  padding: 0.75rem 1rem;
  font-size: 0.95rem;
  color: var(--text-muted);
  border-bottom: 2px solid transparent;
  margin-bottom: -1px;
}
.layer-btn.active {
  color: var(--accent-dark);
  border-bottom-color: var(--accent);
  font-weight: 600;
}
.layer-btn .check {
  color: var(--correct);
  margin-left: 0.3rem;
}

/* App container */
.app {
  max-width: 900px;
  margin: 0 auto;
  padding: 1.75rem 1.5rem 4rem;
}

.card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.25rem 1.4rem;
  margin-bottom: 1.1rem;
  box-shadow: var(--shadow);
}

/* Teaching layer */
.summary-block p {
  font-size: 1.02rem;
}

.question-block {
  margin-top: 1.5rem;
}
.question-block h4 {
  font-family: inherit;
  font-size: 1rem;
  margin-bottom: 0.75rem;
}
.choice-list {
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}
.choice-btn {
  text-align: left;
  border: 1px solid var(--border);
  background: var(--surface);
  border-radius: 8px;
  padding: 0.6rem 0.85rem;
  font-size: 0.95rem;
  color: var(--text);
}
.choice-btn:hover:not(:disabled) {
  border-color: var(--accent);
}
.choice-btn.selected {
  border-color: var(--accent);
  background: var(--accent-soft);
  color: var(--accent-dark);
  font-weight: 600;
}
.choice-btn:disabled { cursor: default; }
.choice-btn.correct {
  background: var(--correct-soft);
  border-color: var(--correct);
  color: var(--correct);
  font-weight: 600;
}
.choice-btn.incorrect {
  background: var(--incorrect-soft);
  border-color: var(--incorrect);
  color: var(--incorrect);
  font-weight: 600;
}
.explanation {
  margin-top: 0.6rem;
  font-size: 0.9rem;
  color: var(--text-muted);
  background: var(--accent-soft);
  border-radius: 8px;
  padding: 0.6rem 0.8rem;
}

/* Flashcards */
.flashcard-wrap {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 1rem;
}
.flashcard {
  width: 100%;
  max-width: 480px;
  min-height: 220px;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--surface);
  box-shadow: var(--shadow);
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  padding: 1.5rem;
  font-size: 1.15rem;
  cursor: pointer;
}
.flashcard .term { font-weight: 700; }
.flashcard .definition { color: var(--text-muted); font-size: 1rem; }
.flashcard-controls {
  display: flex;
  gap: 0.75rem;
}
.flashcard-meta {
  font-size: 0.85rem;
  color: var(--text-muted);
}

/* Buttons */
.btn {
  border: 1px solid var(--accent);
  background: var(--accent);
  color: #fff;
  border-radius: 8px;
  padding: 0.6rem 1.1rem;
  font-size: 0.9rem;
  font-weight: 600;
}
.btn:hover { background: var(--accent-dark); }
.btn.secondary {
  background: var(--surface);
  color: var(--accent-dark);
}
.btn.secondary:hover { background: var(--accent-soft); }
.btn:disabled {
  opacity: 0.5;
  cursor: default;
}

/* Quizzes */
.quiz-picker {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 0.9rem;
}
.quiz-pick-card {
  text-align: left;
}
.quiz-pick-card .score-tag {
  display: inline-block;
  margin-top: 0.5rem;
  font-size: 0.85rem;
  color: var(--text-muted);
}
.quiz-progress {
  font-size: 0.85rem;
  color: var(--text-muted);
  margin-bottom: 1rem;
}
.result-summary {
  font-size: 1.1rem;
  font-weight: 600;
  margin-bottom: 1rem;
}

/* Test */
.free-response textarea {
  width: 100%;
  min-height: 110px;
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 0.7rem;
  font-family: inherit;
  font-size: 0.95rem;
  resize: vertical;
}
.grade-tag {
  display: inline-block;
  padding: 0.15rem 0.55rem;
  border-radius: 6px;
  font-size: 0.8rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.03em;
}
.grade-tag.full { background: var(--correct-soft); color: var(--correct); }
.grade-tag.partial { background: var(--partial-soft); color: var(--partial); }
.grade-tag.none { background: var(--incorrect-soft); color: var(--incorrect); }
.grade-tag.pending { background: var(--border); color: var(--text-muted); }
.loading-line {
  color: var(--text-muted);
  font-size: 0.9rem;
  font-style: italic;
}
.points-list {
  font-size: 0.88rem;
  margin: 0.4rem 0 0;
  padding-left: 1.2rem;
}
.points-list.missed { color: var(--incorrect); }
.points-list.hit { color: var(--correct); }

.footer, .site-footer {
  text-align: center;
  color: var(--text-muted);
  font-size: 0.8rem;
  padding: 2rem 1.5rem;
}

.empty-note {
  color: var(--text-muted);
  font-style: italic;
}

@media (max-width: 600px) {
  .chapter-nav, .layer-nav, .app { padding-left: 1rem; padding-right: 1rem; }
  .layer-nav { overflow-x: auto; }
}