/* ---------- Design tokens ---------- */
:root {
  --bg: #f0eee3;
  --bg-card: #f7f5ec;
  --ink: #2a241d;
  --ink-soft: #6b6558;
  --accent: #c1633d;
  --accent-soft: #e3c9bb;
  --border: #e3dfd0;
  --track: #e6e2d3;
  --serif: "Source Serif 4", "Georgia", serif;
  --sans: "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  --radius: 14px;
  --radius-pill: 999px;
  --max-width: 960px;
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: var(--sans);
  -webkit-font-smoothing: antialiased;
}

body { overflow-x: hidden; }

a { color: inherit; }

img { max-width: 100%; display: block; }

.container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 24px;
}

/* ---------- Header ---------- */
.site-header {
  display: flex;
  align-items: center;
  gap: 24px;
  padding: 18px 24px;
  border-bottom: 1px solid var(--border);
  background: var(--bg);
  position: sticky;
  top: 0;
  z-index: 10;
}

.brand {
  display: flex;
  align-items: center;
  gap: 8px;
  font-weight: 600;
  white-space: nowrap;
  text-decoration: none;
  color: var(--ink);
  cursor: pointer;
  background: none;
  border: none;
  font-family: var(--sans);
  font-size: 1rem;
  padding: 0;
}

.brand-icon { font-size: 1.1rem; }

.progress-track {
  flex: 1;
  height: 4px;
  border-radius: var(--radius-pill);
  background: var(--track);
  overflow: hidden;
}

.progress-fill {
  height: 100%;
  background: var(--accent);
  border-radius: var(--radius-pill);
  transition: width 0.3s ease;
  width: 0%;
}

.header-right {
  display: flex;
  align-items: center;
  gap: 12px;
  white-space: nowrap;
  font-size: 0.85rem;
  color: var(--ink-soft);
  flex-shrink: 0;
}

.btn-pill-outline {
  border: 1px solid var(--border);
  background: transparent;
  color: var(--ink);
  border-radius: var(--radius-pill);
  padding: 7px 16px;
  font-size: 0.85rem;
  cursor: pointer;
  font-family: var(--sans);
  flex-shrink: 0;
}

.btn-pill-outline:hover { border-color: var(--accent); }

@media (max-width: 520px) {
  .site-header { padding: 14px 16px; gap: 10px; }
  .brand { font-size: 0.85rem; overflow: hidden; text-overflow: ellipsis; min-width: 0; }
  .brand-label { display: none; }
  .progress-track { min-width: 36px; flex: 0.4; }
  .header-right { font-size: 0.72rem; gap: 6px; }
  .btn-pill-outline { padding: 5px 10px; font-size: 0.72rem; }
}

/* ---------- Buttons ---------- */
.btn {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  border-radius: var(--radius-pill);
  padding: 12px 24px;
  font-family: var(--sans);
  font-size: 0.95rem;
  font-weight: 600;
  cursor: pointer;
  text-decoration: none;
  border: 1px solid transparent;
}

.btn-primary {
  background: var(--accent);
  color: #fff;
}
.btn-primary:hover { background: #ab5233; }

.btn-outline {
  background: transparent;
  border-color: var(--border);
  color: var(--ink);
}
.btn-outline:hover { border-color: var(--accent); }

.btn:disabled,
.btn-primary:disabled {
  opacity: 0.5;
  cursor: not-allowed;
  background: var(--ink-soft);
}
.btn:disabled:hover { background: var(--ink-soft); }

a:focus-visible,
button:focus-visible,
textarea:focus-visible,
input:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

/* ---------- Eyebrow / headings ---------- */
.eyebrow {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  font-size: 0.75rem;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--ink-soft);
  font-weight: 600;
}
.eyebrow::before {
  content: "";
  display: inline-block;
  width: 18px;
  height: 1px;
  background: var(--ink-soft);
}

h1, h2, h3 { font-family: var(--serif); font-weight: 600; margin: 0; }

.headline {
  font-size: clamp(2.2rem, 5vw, 3.4rem);
  line-height: 1.1;
  margin: 16px 0 20px;
}

.headline em, .accent {
  color: var(--accent);
  font-style: italic;
}

.subline {
  font-family: var(--serif);
  font-style: italic;
  color: var(--ink-soft);
  font-size: 1.15rem;
  line-height: 1.5;
  max-width: 640px;
}

/* ---------- Hero ---------- */
.hero { padding: 64px 0 40px; }

.pills {
  display: flex;
  gap: 10px;
  flex-wrap: wrap;
  margin: 28px 0;
}

.pill {
  border: 1px solid var(--border);
  border-radius: var(--radius-pill);
  padding: 8px 16px;
  font-size: 0.85rem;
  color: var(--ink-soft);
  background: var(--bg-card);
}

.cta-row {
  display: flex;
  gap: 14px;
  flex-wrap: wrap;
  margin-bottom: 28px;
}

/* ---------- Re-entry banner ---------- */
.reentry-banner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  flex-wrap: wrap;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 18px 22px;
  margin-top: 8px;
}

.reentry-banner strong { font-weight: 700; }

/* ---------- Chapter grid ---------- */
.chapter-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 16px;
  margin: 40px 0 80px;
}

@media (max-width: 900px) {
  .chapter-grid { grid-template-columns: repeat(2, 1fr); }
}
@media (max-width: 560px) {
  .chapter-grid { grid-template-columns: 1fr; }
}

.chapter-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 20px;
  text-decoration: none;
  color: inherit;
  display: block;
  transition: border-color 0.15s ease, transform 0.15s ease;
}

.chapter-card:hover:not(.locked) {
  border-color: var(--accent);
  transform: translateY(-2px);
}

.chapter-card.locked {
  opacity: 0.55;
  cursor: not-allowed;
}

.chapter-number {
  font-size: 0.8rem;
  color: var(--ink-soft);
  font-weight: 600;
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.chapter-card h3 {
  font-size: 1.05rem;
  margin: 8px 0 6px;
  display: flex;
  align-items: center;
  gap: 6px;
}

.chapter-card p {
  font-size: 0.85rem;
  color: var(--ink-soft);
  margin: 0;
  line-height: 1.4;
}

.check { color: var(--accent); }
.lock-icon { color: var(--ink-soft); }

/* ---------- Chapter page ---------- */
.chapter-page { padding: 48px 0 96px; }

.chapter-intro {
  font-size: 1.05rem;
  line-height: 1.6;
  color: var(--ink-soft);
  max-width: 680px;
  margin-bottom: 32px;
}

.accordion { margin: 24px 0; }

.accordion-item {
  border: 1px solid var(--border);
  border-radius: var(--radius);
  margin-bottom: 12px;
  background: var(--bg-card);
  overflow: hidden;
}

.accordion-header {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 18px 22px;
  cursor: pointer;
  font-weight: 600;
  background: none;
  border: none;
  width: 100%;
  text-align: left;
  font-family: var(--sans);
  font-size: 1rem;
  color: inherit;
}

.accordion-header .num {
  font-size: 0.75rem;
  color: var(--ink-soft);
  font-weight: 600;
}

.accordion-header .plus {
  margin-left: auto;
  font-size: 1.2rem;
  color: var(--ink-soft);
  transition: transform 0.2s ease;
}

.accordion-item.open .plus { transform: rotate(45deg); }

.accordion-body {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.25s ease;
  padding: 0 22px;
}

.accordion-item.open .accordion-body {
  max-height: 2000px;
  padding: 0 22px 20px;
}

.accordion-body p { line-height: 1.65; color: var(--ink); }
.accordion-body code {
  background: var(--track);
  padding: 2px 6px;
  border-radius: 4px;
  font-size: 0.9em;
}

.code-block {
  position: relative;
  background: #2a241d;
  color: #f0eee3;
  border-radius: 10px;
  padding: 16px 18px;
  font-family: "SF Mono", Menlo, monospace;
  font-size: 0.85rem;
  overflow-x: auto;
  margin: 12px 0;
}

.copy-btn {
  position: absolute;
  top: 10px;
  right: 10px;
  background: rgba(255,255,255,0.12);
  color: #f0eee3;
  border: none;
  border-radius: 6px;
  padding: 4px 10px;
  font-size: 0.75rem;
  cursor: pointer;
}

/* ---------- Reflection ---------- */
.reflection-box {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 24px;
  margin: 32px 0;
}

.reflection-box label {
  display: block;
  font-weight: 600;
  margin-bottom: 10px;
}

.reflection-box textarea {
  width: 100%;
  min-height: 100px;
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 12px 14px;
  font-family: var(--sans);
  font-size: 0.95rem;
  background: #fff;
  resize: vertical;
}

.reflection-hint {
  font-size: 0.8rem;
  color: var(--ink-soft);
  margin-top: 8px;
}

/* ---------- Quiz ---------- */
.quiz-box {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 28px;
  margin: 32px 0;
}

.quiz-question { margin-bottom: 24px; }
.quiz-question p.q-text { font-weight: 600; margin: 0 0 12px; }

.quiz-option {
  display: block;
  width: 100%;
  text-align: left;
  border: 1px solid var(--border);
  background: #fff;
  border-radius: 10px;
  padding: 12px 16px;
  margin-bottom: 8px;
  cursor: pointer;
  font-family: var(--sans);
  font-size: 0.92rem;
}

.quiz-option.selected { border-color: var(--accent); background: var(--accent-soft); }
.quiz-option.correct { border-color: #4a7a4a; background: #e2ecdf; }
.quiz-option.incorrect { border-color: #a3453a; background: #f2ddd9; }

.quiz-result {
  margin-top: 16px;
  padding: 16px;
  border-radius: 10px;
  background: #fff;
  border: 1px solid var(--border);
  display: none;
}

.quiz-result.show { display: block; }
.quiz-result.pass { border-color: #4a7a4a; }
.quiz-result.fail { border-color: #a3453a; }

/* ---------- Slider / calculator (chapter 3) ---------- */
.calc-box {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 24px;
  margin: 24px 0;
}

.calc-box input[type="range"] { width: 100%; margin: 12px 0; accent-color: var(--accent); }

.calc-results {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 12px;
  margin-top: 16px;
}

@media (max-width: 560px) {
  .calc-results { grid-template-columns: 1fr; }
}

.calc-result-card {
  background: #fff;
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 14px;
  text-align: center;
}

.calc-result-card .model-name { font-weight: 700; font-size: 0.9rem; }
.calc-result-card .price { font-family: var(--serif); font-size: 1.4rem; color: var(--accent); margin-top: 4px; }

/* ---------- Toggle diagram ---------- */
.toggle-box {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 24px;
  margin: 24px 0;
}

.toggle-switch {
  display: flex;
  gap: 8px;
  margin-bottom: 20px;
}

.toggle-switch button {
  flex: 1;
  padding: 10px 16px;
  border-radius: var(--radius-pill);
  border: 1px solid var(--border);
  background: #fff;
  font-family: var(--sans);
  font-weight: 600;
  font-size: 0.9rem;
  cursor: pointer;
  color: var(--ink-soft);
}

.toggle-switch button.active {
  background: var(--accent);
  border-color: var(--accent);
  color: #fff;
}

.toggle-diagram {
  min-height: 160px;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 20px 0;
}

.toggle-caption {
  font-size: 0.9rem;
  color: var(--ink-soft);
  line-height: 1.6;
  margin-top: 12px;
}

.diagram-node {
  border: 2px solid var(--accent);
  border-radius: 10px;
  padding: 10px 16px;
  background: #fff;
  font-size: 0.85rem;
  font-weight: 600;
  text-align: center;
}

.diagram-node.main { border-color: var(--ink); }

.diagram-row {
  display: flex;
  gap: 14px;
  align-items: center;
  justify-content: center;
  flex-wrap: wrap;
}

.diagram-col {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 10px;
}

.diagram-arrow {
  color: var(--ink-soft);
  font-size: 1.2rem;
}

.diagram-link {
  width: 1px;
  height: 24px;
  background: var(--border);
}

/* ---------- Locked notice ---------- */
.locked-notice {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 18px 22px;
  margin: 24px 0;
}

/* ---------- Footer ---------- */
.site-footer {
  text-align: center;
  padding: 40px 0;
  color: var(--ink-soft);
  font-size: 0.8rem;
}

.reset-link {
  background: none;
  border: none;
  color: var(--ink-soft);
  text-decoration: underline;
  cursor: pointer;
  font-size: 0.8rem;
  font-family: var(--sans);
}

/* ---------- Nav footer (prev/next) ---------- */
.chapter-nav {
  display: flex;
  justify-content: space-between;
  margin-top: 40px;
  gap: 16px;
}