:root {
  --ink: #1c2733;
  --ink-soft: #4a5768;
  --paper: #faf8f4;
  --card: #ffffff;
  --accent: #a8442c;
  --accent-soft: #f1e3dc;
  --good: #2f7a4f;
  --bad: #b3372c;
  --border: #e4ddd2;
  --radius: 10px;
  font-size: 17px;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  background: var(--paper);
  color: var(--ink);
  line-height: 1.5;
}

header.site-header {
  padding: 2rem 1.5rem 1.5rem;
  border-bottom: 1px solid var(--border);
  background: var(--card);
}

header.site-header h1 {
  margin: 0 0 0.25rem;
  font-size: 1.6rem;
}

header.site-header p {
  margin: 0;
  color: var(--ink-soft);
}

main {
  max-width: 900px;
  margin: 0 auto;
  padding: 1.5rem;
}

a.back-link {
  display: inline-block;
  margin-bottom: 1rem;
  color: var(--accent);
  text-decoration: none;
  font-weight: 600;
}
a.back-link:hover { text-decoration: underline; }

.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: 1rem;
}

.subunit-card {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.25rem;
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.subunit-card h2 {
  margin: 0;
  font-size: 1.15rem;
}

.subunit-card .meta {
  color: var(--ink-soft);
  font-size: 0.9rem;
}

.badge {
  align-self: flex-start;
  font-size: 0.75rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.03em;
  padding: 0.2rem 0.55rem;
  border-radius: 999px;
  background: var(--accent-soft);
  color: var(--accent);
}

.subunit-card .study-btn {
  margin-top: 0.5rem;
  display: inline-block;
  text-align: center;
  background: var(--accent);
  color: #fff;
  text-decoration: none;
  padding: 0.55rem 1rem;
  border-radius: var(--radius);
  font-weight: 600;
}
.subunit-card .study-btn:hover { opacity: 0.9; }

section.block {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.25rem 1.5rem;
  margin-bottom: 1.5rem;
}

section.block h2 {
  margin-top: 0;
  font-size: 1.2rem;
  border-bottom: 1px solid var(--border);
  padding-bottom: 0.5rem;
}

.study-header h1 { margin-bottom: 0.15rem; }
.study-header .meta { color: var(--ink-soft); margin-bottom: 1.5rem; }

ul.key-points { padding-left: 1.2rem; margin: 0; }
ul.key-points li { margin-bottom: 0.55rem; }

.timeline { list-style: none; padding: 0; margin: 0; }
.timeline li {
  display: grid;
  grid-template-columns: 110px 1fr;
  gap: 0.75rem;
  padding: 0.5rem 0;
  border-bottom: 1px dashed var(--border);
}
.timeline li:last-child { border-bottom: none; }
.timeline .date { font-weight: 700; color: var(--accent); }

/* Flashcards */
.flashcard-wrap {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 1rem;
}

.flashcard {
  width: 100%;
  max-width: 520px;
  min-height: 160px;
  perspective: 1200px;
  cursor: pointer;
}

.flashcard-inner {
  position: relative;
  width: 100%;
  height: 100%;
  min-height: 160px;
  transition: transform 0.5s;
  transform-style: preserve-3d;
}

.flashcard.flipped .flashcard-inner { transform: rotateY(180deg); }

.flashcard-face {
  position: absolute;
  inset: 0;
  backface-visibility: hidden;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  padding: 1.5rem;
  border-radius: var(--radius);
  border: 1px solid var(--border);
  font-size: 1.05rem;
}

.flashcard-face.front { background: var(--accent-soft); font-weight: 700; }
.flashcard-face.back { background: var(--card); transform: rotateY(180deg); }

.flashcard-controls {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

button {
  font: inherit;
  cursor: pointer;
  border: 1px solid var(--border);
  background: var(--card);
  color: var(--ink);
  padding: 0.5rem 1rem;
  border-radius: var(--radius);
}
button.primary { background: var(--accent); color: #fff; border-color: var(--accent); }
button:hover { filter: brightness(0.97); }
button:disabled { opacity: 0.5; cursor: default; }

.flashcard-progress { color: var(--ink-soft); font-size: 0.9rem; }

/* Quiz */
.quiz-progress { color: var(--ink-soft); font-size: 0.9rem; margin-bottom: 0.75rem; }
.quiz-question { font-weight: 700; margin-bottom: 0.9rem; }

.quiz-choices { display: flex; flex-direction: column; gap: 0.55rem; margin-bottom: 1rem; }

.quiz-choice {
  text-align: left;
  padding: 0.65rem 0.9rem;
  border-radius: var(--radius);
  border: 1px solid var(--border);
  background: var(--card);
}
.quiz-choice.correct { background: #e5f3ea; border-color: var(--good); color: var(--good); }
.quiz-choice.incorrect { background: #fbe8e5; border-color: var(--bad); color: var(--bad); }
.quiz-choice.disabled { cursor: default; }

.quiz-explanation {
  background: var(--accent-soft);
  border-radius: var(--radius);
  padding: 0.75rem 1rem;
  margin-bottom: 1rem;
  font-size: 0.95rem;
}

.quiz-score {
  text-align: center;
  padding: 1.5rem;
}
.quiz-score .score-big {
  font-size: 2.2rem;
  font-weight: 800;
  color: var(--accent);
}

.empty-state { color: var(--ink-soft); text-align: center; padding: 2rem; }