/* ============================================================
   Sustainability Economics — Study Site
   Shared styles (adapted from Corporate Finance study site)
   Accent colour changed: blue → green
   ============================================================ */

:root {
  --bg: #0f172a;
  --bg-2: #1e293b;
  --panel: #ffffff;
  --panel-2: #f8fafc;
  --panel-3: #f1f5f9;
  --border: #e2e8f0;
  --text: #0f172a;
  --text-2: #475569;
  --text-3: #64748b;
  --accent: #16a34a;
  --accent-2: #15803d;
  --accent-soft: #dcfce7;
  --good: #16a34a;
  --good-soft: #dcfce7;
  --bad: #dc2626;
  --bad-soft: #fee2e2;
  --warn: #d97706;
  --warn-soft: #fef3c7;
  --purple: #7c3aed;
  --purple-soft: #ede9fe;
  --shadow-sm: 0 1px 2px rgba(15, 23, 42, 0.06);
  --shadow: 0 4px 12px rgba(15, 23, 42, 0.08);
  --shadow-lg: 0 12px 32px rgba(15, 23, 42, 0.12);
  --radius: 12px;
  --radius-sm: 8px;
  --radius-lg: 18px;
  --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --font-serif: "Iowan Old Style", "Palatino Linotype", Palatino, Georgia, serif;
  --font-mono: "SF Mono", Menlo, Consolas, "Liberation Mono", monospace;
}

[data-theme="dark"] {
  --bg: #020617;
  --bg-2: #0f172a;
  --panel: #1e293b;
  --panel-2: #0f172a;
  --panel-3: #1e293b;
  --border: #334155;
  --text: #f1f5f9;
  --text-2: #cbd5e1;
  --text-3: #94a3b8;
  --accent: #4ade80;
  --accent-2: #86efac;
  --accent-soft: #14532d;
  --good-soft: #14532d;
  --bad-soft: #7f1d1d;
  --warn-soft: #78350f;
  --purple-soft: #4c1d95;
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  font-family: var(--font-sans);
  font-size: 16px;
  line-height: 1.6;
  color: var(--text);
  background: var(--panel-2);
  -webkit-font-smoothing: antialiased;
}

a {
  color: var(--accent);
  text-decoration: none;
}
a:hover { text-decoration: underline; }

/* ---------- Layout ---------- */

.topbar {
  position: sticky;
  top: 0;
  z-index: 50;
  background: var(--panel);
  border-bottom: 1px solid var(--border);
  padding: 0.75rem 1.25rem;
  display: flex;
  align-items: center;
  gap: 1rem;
  box-shadow: var(--shadow-sm);
}
.topbar .brand {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  font-weight: 700;
  font-size: 1.05rem;
  color: var(--text);
}
.topbar .brand .dot {
  width: 12px; height: 12px; border-radius: 50%;
  background: linear-gradient(135deg, var(--accent), var(--purple));
}
.topbar .crumbs {
  color: var(--text-3);
  font-size: 0.9rem;
}
.topbar .crumbs a { color: var(--text-2); }
.topbar .spacer { flex: 1; }
.topbar .controls { display: flex; gap: 0.5rem; }
.topbar .controls button {
  background: var(--panel-3);
  border: 1px solid var(--border);
  color: var(--text-2);
  padding: 0.4rem 0.75rem;
  border-radius: var(--radius-sm);
  font-size: 0.85rem;
  cursor: pointer;
}
.topbar .controls button:hover { background: var(--accent-soft); color: var(--accent-2); border-color: var(--accent); }

.shell { max-width: 1200px; margin: 0 auto; padding: 1.5rem 1.25rem 4rem; }

/* ---------- Index page ---------- */

.hero {
  background: linear-gradient(135deg, #14532d 0%, #166534 50%, #4c1d95 100%);
  color: white;
  border-radius: var(--radius-lg);
  padding: 2.5rem 2rem;
  margin-bottom: 2rem;
  box-shadow: var(--shadow);
}
.hero h1 { font-family: var(--font-serif); font-size: 2.2rem; margin: 0 0 0.5rem; }
.hero p { font-size: 1.05rem; margin: 0; opacity: 0.9; max-width: 680px; }

.chapter-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 1rem;
}
.chapter-card {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.25rem;
  display: flex; flex-direction: column;
  text-decoration: none;
  color: var(--text);
  transition: transform 0.12s, box-shadow 0.12s, border-color 0.12s;
  box-shadow: var(--shadow-sm);
  min-height: 160px;
}
.chapter-card:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow);
  border-color: var(--accent);
  text-decoration: none;
}
.chapter-card.disabled { opacity: 0.5; cursor: not-allowed; pointer-events: none; }
.chapter-card .num {
  font-family: var(--font-serif);
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--accent);
  letter-spacing: 0.06em;
  text-transform: uppercase;
  margin-bottom: 0.25rem;
}
.chapter-card .title {
  font-size: 1.15rem;
  font-weight: 600;
  margin-bottom: 0.5rem;
  font-family: var(--font-serif);
}
.chapter-card .blurb { color: var(--text-3); font-size: 0.92rem; flex: 1; }
.chapter-card .status {
  margin-top: 0.75rem;
  font-size: 0.8rem;
  color: var(--text-3);
  display: flex;
  align-items: center;
  gap: 0.4rem;
}
.status .badge {
  display: inline-block;
  padding: 0.15rem 0.5rem;
  border-radius: 999px;
  font-weight: 500;
  font-size: 0.7rem;
}
.badge.ready { background: var(--good-soft); color: var(--good); }
.badge.todo { background: var(--panel-3); color: var(--text-3); }
.badge.partial { background: var(--warn-soft); color: var(--warn); }

/* ---------- Chapter pages ---------- */

.chapter-shell {
  display: grid;
  grid-template-columns: 240px 1fr;
  gap: 2rem;
  align-items: start;
}
@media (max-width: 900px) {
  .chapter-shell { grid-template-columns: 1fr; }
  .sidenav { position: static !important; }
}

.sidenav {
  position: sticky;
  top: 5rem;
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1rem;
  font-size: 0.9rem;
}
.sidenav h4 {
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-3);
  margin: 0 0 0.5rem;
}
.sidenav ol {
  list-style: none;
  padding: 0;
  margin: 0;
  counter-reset: nav;
}
.sidenav li { margin: 0.15rem 0; counter-increment: nav; }
.sidenav a {
  display: block;
  padding: 0.4rem 0.6rem;
  color: var(--text-2);
  border-radius: var(--radius-sm);
  border-left: 2px solid transparent;
  font-size: 0.88rem;
}
.sidenav a:before {
  content: counter(nav) ". ";
  color: var(--text-3);
  margin-right: 0.2rem;
}
.sidenav a:hover { background: var(--accent-soft); color: var(--accent-2); text-decoration: none; }
.sidenav a.active { background: var(--accent-soft); color: var(--accent-2); border-left-color: var(--accent); font-weight: 600; }

.main-col { min-width: 0; }

.chapter-header {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.75rem 1.75rem 1.25rem;
  margin-bottom: 1.5rem;
  box-shadow: var(--shadow-sm);
}
.chapter-header .label {
  font-size: 0.8rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--accent);
  font-weight: 600;
}
.chapter-header h1 {
  font-family: var(--font-serif);
  font-size: 2rem;
  margin: 0.25rem 0 0.5rem;
}
.chapter-header .lede {
  font-size: 1.02rem;
  color: var(--text-2);
  margin: 0;
}
.chapter-header .meta {
  margin-top: 1rem;
  display: flex; flex-wrap: wrap; gap: 0.5rem;
}
.meta .chip {
  background: var(--panel-3);
  color: var(--text-2);
  padding: 0.25rem 0.65rem;
  border-radius: 999px;
  font-size: 0.78rem;
}

section.block {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.5rem 1.75rem;
  margin-bottom: 1.25rem;
  box-shadow: var(--shadow-sm);
}
section.block > h2 {
  font-family: var(--font-serif);
  font-size: 1.5rem;
  margin: 0 0 0.25rem;
  display: flex; align-items: baseline; gap: 0.6rem;
}
section.block > h2 .sect-num {
  color: var(--text-3);
  font-size: 0.85rem;
  font-weight: 500;
  font-family: var(--font-sans);
}
section.block > .section-intro {
  color: var(--text-2);
  margin: 0.25rem 0 1rem;
}
section.block h3 {
  font-family: var(--font-serif);
  font-size: 1.2rem;
  margin: 1.5rem 0 0.5rem;
  color: var(--text);
}
section.block h4 {
  font-size: 1.02rem;
  margin: 1rem 0 0.3rem;
  color: var(--text);
}
section.block p { margin: 0.5rem 0; }
section.block ul, section.block ol { padding-left: 1.4rem; margin: 0.5rem 0; }
section.block li { margin: 0.3rem 0; }
section.block strong { color: var(--text); }

/* ---------- Reusable content blocks ---------- */

.callout {
  background: var(--accent-soft);
  border-left: 4px solid var(--accent);
  border-radius: var(--radius-sm);
  padding: 0.9rem 1.1rem;
  margin: 1rem 0;
}
.callout.warn { background: var(--warn-soft); border-color: var(--warn); }
.callout.good { background: var(--good-soft); border-color: var(--good); }
.callout.purple { background: var(--purple-soft); border-color: var(--purple); }
.callout .label {
  font-size: 0.72rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  font-weight: 700;
  margin-bottom: 0.25rem;
  color: var(--accent-2);
}
.callout.warn .label { color: var(--warn); }
.callout.good .label { color: var(--good); }
.callout.purple .label { color: var(--purple); }
.callout p:last-child { margin-bottom: 0; }

.tag {
  display: inline-block;
  background: var(--panel-3);
  color: var(--text-2);
  padding: 0.1rem 0.55rem;
  border-radius: 999px;
  font-size: 0.72rem;
  font-weight: 500;
}
.tag.accent { background: var(--accent-soft); color: var(--accent-2); }
.tag.good { background: var(--good-soft); color: var(--good); }
.tag.warn { background: var(--warn-soft); color: var(--warn); }
.tag.purple { background: var(--purple-soft); color: var(--purple); }

.kv-table {
  width: 100%;
  border-collapse: collapse;
  margin: 0.75rem 0;
  font-size: 0.95rem;
}
.kv-table th, .kv-table td {
  text-align: left;
  padding: 0.6rem 0.8rem;
  border-bottom: 1px solid var(--border);
  vertical-align: top;
}
.kv-table th {
  background: var(--panel-3);
  font-weight: 600;
  color: var(--text-2);
  font-size: 0.85rem;
}
.kv-table tr:last-child td { border-bottom: none; }

.concept-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  gap: 0.75rem;
  margin: 0.75rem 0;
}
.concept-card {
  background: var(--panel-2);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 0.9rem 1rem;
}
.concept-card .ttl {
  font-weight: 600;
  margin-bottom: 0.3rem;
  font-size: 0.98rem;
  color: var(--text);
}
.concept-card .body { font-size: 0.9rem; color: var(--text-2); }

/* ---------- Diagrams ---------- */

.diagram {
  background: var(--panel-2);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 1rem;
  margin: 1rem 0;
  text-align: center;
}
.diagram svg { max-width: 100%; height: auto; }
.diagram .caption {
  font-size: 0.85rem;
  color: var(--text-3);
  margin-top: 0.6rem;
  text-align: center;
}

/* ---------- Foot nav ---------- */

.footnav {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  margin-top: 2rem;
}
.footnav a {
  flex: 1;
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1rem 1.25rem;
  color: var(--text);
}
.footnav a:hover { border-color: var(--accent); text-decoration: none; }
.footnav .dir { font-size: 0.75rem; color: var(--text-3); }
.footnav .ttl { font-weight: 600; }
.footnav .right { text-align: right; }

/* ---------- Misc ---------- */

.divider {
  height: 1px;
  background: var(--border);
  margin: 1.25rem 0;
  border: none;
}

.quote {
  font-family: var(--font-serif);
  font-style: italic;
  color: var(--text-2);
  border-left: 3px solid var(--text-3);
  padding-left: 1rem;
  margin: 1rem 0;
}
.quote cite {
  display: block;
  font-style: normal;
  color: var(--text-3);
  font-size: 0.85rem;
  margin-top: 0.3rem;
  font-family: var(--font-sans);
}

mark {
  background: linear-gradient(120deg, var(--warn-soft) 0%, var(--warn-soft) 100%);
  color: inherit;
  padding: 0.05em 0.2em;
  border-radius: 3px;
}

/* ---------- Math display ---------- */

.math-block {
  overflow-x: auto;
  padding: 0.5rem 0;
}