:root {
  /* Academic-but-energetic palette: deep navy, bright amber/gold, clean whites */
  --c-navy:        #0b1d3a;
  --c-navy-deep:   #06122a;
  --c-navy-soft:   #1b3060;
  --c-navy-line:   #2a3b69;
  --c-amber:       #f5b301;
  --c-amber-deep:  #d49a00;
  --c-amber-soft:  #fff7df;
  --c-cream:       #fbf6e9;
  --c-paper:       #ffffff;
  --c-bg:          #f7f7f3;
  --c-ink:         #0f1d3a;
  --c-ink-soft:    #475579;
  --c-muted:       #6b7591;
  --c-line:        #e6e2d5;
  --c-line-soft:   #efece2;
  --c-success:     #1a7f5a;
  --c-danger:      #b3261e;

  --font-sans:  "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif;
  --font-serif: "Source Serif 4", "Source Serif Pro", Georgia, "Times New Roman", serif;
  --font-display: "Playfair Display", "Source Serif 4", Georgia, serif;

  --shadow-sm: 0 1px 2px rgba(11, 29, 58, 0.06);
  --shadow-md: 0 8px 24px rgba(11, 29, 58, 0.10);
  --shadow-lg: 0 24px 60px rgba(11, 29, 58, 0.16);

  --radius:    10px;
  --radius-lg: 16px;
  --maxw:      1200px;
}

* { box-sizing: border-box; }
html, body { margin: 0; padding: 0; }
body {
  font-family: var(--font-serif);
  font-size: 17px;
  color: var(--c-ink);
  background: var(--c-bg);
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}
img { max-width: 100%; height: auto; display: block; }

a { color: var(--c-navy); text-decoration: underline; text-decoration-color: var(--c-amber); text-underline-offset: 3px; }
a:hover { color: var(--c-navy-soft); text-decoration-color: var(--c-amber-deep); }

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

.skip { position: absolute; left: -9999px; }
.skip:focus { left: 12px; top: 12px; padding: 8px 12px; background: var(--c-navy); color: #fff; border-radius: 6px; z-index: 100; }

/* ---------- Topbar ---------- */
.topbar {
  background: var(--c-navy-deep);
  color: #cfd6e8;
  font-family: var(--font-sans);
  font-size: 0.82rem;
  letter-spacing: 0.02em;
}
.topbar-inner { display: flex; justify-content: space-between; align-items: center; padding: 8px 24px; }
.topbar-links a { color: #e6ebf7; text-decoration: none; margin-left: 18px; }
.topbar-links a:hover { color: var(--c-amber); }

/* ---------- Header ---------- */
.site-header {
  background: var(--c-navy);
  color: #fff;
  border-bottom: 4px solid var(--c-amber);
  position: sticky; top: 0; z-index: 60;
  box-shadow: var(--shadow-md);
}
.header-inner { display: flex; align-items: center; justify-content: space-between; gap: 24px; padding: 16px 24px; }
.brand { display: inline-flex; align-items: center; gap: 12px; color: #fff; text-decoration: none; }
.brand:hover { text-decoration: none; }
.brand-mark {
  display: inline-grid; place-items: center;
  width: 44px; height: 44px;
  background: var(--c-amber); color: var(--c-navy);
  border-radius: 8px;
  font-family: var(--font-display); font-weight: 800; letter-spacing: 0.5px;
  font-size: 1.15rem;
  box-shadow: 0 2px 0 rgba(0,0,0,0.18);
}
.brand-text { display: inline-flex; flex-direction: column; line-height: 1.05; }
.brand-name { font-family: var(--font-display); font-weight: 800; font-size: 1.45rem; letter-spacing: 0.01em; color: #fff; }
.brand-tag { font-family: var(--font-sans); font-weight: 500; font-size: 0.72rem; color: var(--c-amber); letter-spacing: 0.18em; text-transform: uppercase; margin-top: 2px; }

.primary-nav { display: flex; gap: 4px; flex-wrap: wrap; font-family: var(--font-sans); }
.primary-nav a {
  color: #e6ebf7; padding: 8px 12px; border-radius: 6px; font-weight: 500; font-size: 0.92rem; text-decoration: none;
  transition: background-color .15s ease, color .15s ease;
}
.primary-nav a:hover { background: var(--c-navy-soft); color: #fff; }
.primary-nav a.primary { color: var(--c-navy); background: var(--c-amber); font-weight: 700; }
.primary-nav a.primary:hover { background: var(--c-amber-deep); }

/* ---------- Breadcrumbs ---------- */
.breadcrumbs { background: transparent; padding: 18px 0 0; font-family: var(--font-sans); }
.breadcrumbs ol { list-style: none; padding: 0; margin: 0; display: flex; flex-wrap: wrap; gap: 6px; font-size: 0.84rem; color: var(--c-muted); }
.breadcrumbs li + li::before { content: "›"; margin-right: 6px; color: var(--c-muted); }
.breadcrumbs a { color: var(--c-muted); text-decoration: none; }
.breadcrumbs a:hover { color: var(--c-navy); }
.breadcrumbs span[aria-current] { color: var(--c-navy); font-weight: 600; }

/* ---------- Layout ---------- */
.main-grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 320px;
  gap: 44px;
  margin-top: 28px; margin-bottom: 72px;
}
@media (max-width: 980px) { .main-grid { grid-template-columns: 1fr; gap: 32px; } }

.content { min-width: 0; }
.content h1 {
  font-family: var(--font-display); font-weight: 800; font-size: 2.4rem; line-height: 1.15;
  margin: 0 0 14px; color: var(--c-navy); letter-spacing: -0.005em;
}
.content h2 {
  font-family: var(--font-display); font-weight: 700; font-size: 1.55rem; line-height: 1.2;
  margin: 40px 0 14px; color: var(--c-navy); padding-bottom: 8px; border-bottom: 2px solid var(--c-line-soft);
}
.content h3 { font-family: var(--font-sans); font-weight: 700; font-size: 1.12rem; margin: 26px 0 8px; color: var(--c-navy); letter-spacing: -0.005em; }
.content h4 { font-family: var(--font-sans); font-weight: 700; font-size: 1rem; margin: 18px 0 6px; color: var(--c-navy); }
.content p { margin: 0 0 14px; }
.content ul, .content ol { padding-left: 22px; margin: 0 0 16px; }
.content li { margin-bottom: 5px; }
.content strong { color: var(--c-navy); }
.lead { font-family: var(--font-serif); font-size: 1.18rem; color: var(--c-ink-soft); line-height: 1.55; margin: 0 0 22px; }

/* ---------- Sidebar ---------- */
.sidebar { display: flex; flex-direction: column; gap: 18px; font-family: var(--font-sans); }
.card {
  background: var(--c-paper);
  border: 1px solid var(--c-line);
  border-radius: var(--radius);
  padding: 20px;
  box-shadow: var(--shadow-sm);
}
.card h3 { font-family: var(--font-sans); margin: 0 0 6px; font-size: 1rem; color: var(--c-navy); font-weight: 700; }
.card p { margin: 0 0 12px; color: var(--c-ink-soft); font-size: 0.92rem; line-height: 1.5; }
.card.subtle { background: transparent; border: 1px dashed var(--c-line); box-shadow: none; }
.card.card-accent { background: linear-gradient(160deg, var(--c-navy) 0%, var(--c-navy-soft) 100%); color: #fff; border-color: var(--c-navy-soft); }
.card.card-accent h3 { color: var(--c-amber); }
.card.card-accent p { color: #d8dff0; }
.card.card-accent .btn { background: var(--c-amber); color: var(--c-navy); }
.card.card-accent .btn:hover { background: var(--c-amber-deep); }
.card.card-recommend { border-top: 4px solid var(--c-amber); }
.bare { list-style: none; padding: 0; margin: 0; }
.bare li { margin-bottom: 8px; font-size: 0.93rem; }
.bare a { color: var(--c-navy); text-decoration: none; border-bottom: 1px solid transparent; }
.bare a:hover { border-bottom-color: var(--c-amber); color: var(--c-navy-soft); }

.reco li {
  display: flex; flex-direction: column; gap: 2px;
  padding: 10px 0; border-bottom: 1px solid var(--c-line-soft);
}
.reco li:last-child { border-bottom: none; padding-bottom: 0; }
.reco a { font-family: var(--font-serif); font-size: 0.97rem; line-height: 1.35; color: var(--c-navy); text-decoration: none; font-weight: 500; }
.reco a:hover { color: var(--c-navy-soft); text-decoration: underline; text-decoration-color: var(--c-amber); }
.reco-meta { font-size: 0.72rem; color: var(--c-muted); text-transform: uppercase; letter-spacing: 0.08em; }

/* ---------- Buttons ---------- */
.btn {
  display: inline-block; padding: 11px 18px; background: var(--c-amber); color: var(--c-navy);
  border-radius: 8px; font-family: var(--font-sans); font-weight: 700; font-size: 0.94rem; text-decoration: none;
  border: none; cursor: pointer; box-shadow: 0 2px 0 rgba(0,0,0,0.12);
  transition: transform .08s ease, background-color .15s ease;
}
.btn:hover { background: var(--c-amber-deep); text-decoration: none; transform: translateY(-1px); color: var(--c-navy); }
.btn.secondary { background: var(--c-navy); color: #fff; }
.btn.secondary:hover { background: var(--c-navy-soft); color: #fff; }
.btn.ghost { background: transparent; color: var(--c-navy); border: 1.5px solid var(--c-navy); box-shadow: none; }
.btn.ghost:hover { background: var(--c-navy); color: #fff; }
.btn.lg { padding: 14px 24px; font-size: 1rem; }

/* ---------- Hero (home + category) ---------- */
.hero {
  background: linear-gradient(135deg, var(--c-navy-deep) 0%, var(--c-navy) 60%, var(--c-navy-soft) 100%);
  color: #fff;
  border-radius: var(--radius-lg);
  overflow: hidden;
  margin-bottom: 32px;
  box-shadow: var(--shadow-lg);
  position: relative;
  isolation: isolate;
}
.hero::before {
  content: "";
  position: absolute; inset: 0;
  background:
    radial-gradient(800px 300px at 90% -10%, rgba(245,179,1,0.18), transparent 60%),
    radial-gradient(400px 240px at -10% 110%, rgba(245,179,1,0.10), transparent 60%);
  z-index: -1;
}
.hero-grid { display: grid; grid-template-columns: 1.2fr 1fr; align-items: stretch; }
@media (max-width: 880px) { .hero-grid { grid-template-columns: 1fr; } }
.hero-text { padding: 48px 44px; }
.hero-eyebrow {
  display: inline-block; font-family: var(--font-sans); font-size: 0.78rem; font-weight: 600;
  letter-spacing: 0.18em; text-transform: uppercase; color: var(--c-amber);
  border: 1px solid rgba(245,179,1,0.5); padding: 5px 10px; border-radius: 999px; margin-bottom: 18px;
}
.hero-text h1 {
  font-family: var(--font-display); font-weight: 800; color: #fff;
  font-size: clamp(2rem, 4vw, 3.2rem); line-height: 1.08; margin: 0 0 14px; letter-spacing: -0.015em;
}
.hero-text h1 .accent { color: var(--c-amber); }
.hero-text .lead { color: #d8dff0; font-size: 1.12rem; max-width: 56ch; margin-bottom: 24px; }
.hero-cta { display: flex; gap: 12px; flex-wrap: wrap; }
.hero-image { position: relative; min-height: 320px; }
.hero-image img { width: 100%; height: 100%; object-fit: cover; }
.hero-image::after {
  content: ""; position: absolute; inset: 0;
  background: linear-gradient(110deg, var(--c-navy) 0%, transparent 30%);
  pointer-events: none;
}
@media (max-width: 880px) { .hero-image { min-height: 220px; } }

.hero-stats { display: grid; grid-template-columns: repeat(4, 1fr); gap: 0; border-top: 1px solid rgba(255,255,255,0.10); }
.hero-stat { padding: 18px 24px; border-right: 1px solid rgba(255,255,255,0.10); font-family: var(--font-sans); }
.hero-stat:last-child { border-right: none; }
.hero-stat .num { font-family: var(--font-display); font-weight: 800; color: var(--c-amber); font-size: 1.6rem; line-height: 1; display: block; }
.hero-stat .lbl { font-size: 0.78rem; color: #cfd6e8; text-transform: uppercase; letter-spacing: 0.1em; margin-top: 4px; display: block; }
@media (max-width: 700px) { .hero-stats { grid-template-columns: repeat(2, 1fr); } .hero-stat:nth-child(2n) { border-right: none; } }

/* ---------- Eyebrow & section ---------- */
.eyebrow {
  font-family: var(--font-sans); text-transform: uppercase; letter-spacing: 0.12em;
  font-size: 0.74rem; color: var(--c-amber-deep); font-weight: 700;
}
.section { margin: 36px 0; }
.section h2 { margin-top: 0; }
.section-head { display: flex; align-items: baseline; justify-content: space-between; flex-wrap: wrap; gap: 12px; margin-bottom: 12px; }
.section-head h2 { margin: 0; border: none; padding: 0; }
.section-head .meta { font-family: var(--font-sans); color: var(--c-muted); font-size: 0.88rem; }

/* ---------- Tiles (subject / category cards) ---------- */
.tiles { display: grid; grid-template-columns: repeat(auto-fill, minmax(240px, 1fr)); gap: 14px; margin: 16px 0 24px; }
.tile {
  display: block; padding: 18px 20px; background: var(--c-paper); border: 1px solid var(--c-line);
  border-radius: var(--radius); color: var(--c-ink); text-decoration: none;
  transition: transform .12s ease, box-shadow .12s ease, border-color .12s ease;
  position: relative; border-left: 3px solid var(--c-line);
}
.tile:hover { transform: translateY(-2px); box-shadow: var(--shadow-md); text-decoration: none; border-left-color: var(--c-amber); border-color: var(--c-line); }
.tile h3 { font-family: var(--font-display); font-weight: 700; margin: 0 0 4px; color: var(--c-navy); font-size: 1.08rem; }
.tile p { margin: 0; color: var(--c-muted); font-size: 0.88rem; font-family: var(--font-sans); }

.tile-cat {
  background: linear-gradient(180deg, var(--c-paper) 0%, var(--c-cream) 100%);
  border-left: 4px solid var(--c-amber);
}

/* ---------- Unit list ---------- */
.unit-list { display: grid; gap: 8px; padding: 0; list-style: none; margin: 0; counter-reset: unit; }
.unit-list a {
  display: flex; justify-content: space-between; align-items: center; gap: 16px;
  background: var(--c-paper); border: 1px solid var(--c-line); border-radius: var(--radius);
  padding: 14px 18px; color: var(--c-ink); text-decoration: none;
  transition: border-color .12s ease, transform .08s ease;
}
.unit-list a:hover { border-color: var(--c-navy); transform: translateX(2px); }
.unit-list .num {
  display: inline-grid; place-items: center; min-width: 38px; height: 38px;
  background: var(--c-amber-soft); color: var(--c-navy); border-radius: 8px;
  font-family: var(--font-display); font-weight: 800; margin-right: 14px; font-variant-numeric: tabular-nums;
}
.unit-list .uname { font-family: var(--font-serif); font-weight: 500; color: var(--c-navy); }
.unit-list .meta { font-family: var(--font-sans); color: var(--c-muted); font-size: 0.85rem; white-space: nowrap; }

/* ---------- Question (practice items) ---------- */
.question { background: var(--c-paper); border: 1px solid var(--c-line); border-radius: var(--radius); padding: 22px; margin: 16px 0; box-shadow: var(--shadow-sm); }
.question h4 { margin: 0 0 10px; font-family: var(--font-sans); color: var(--c-amber-deep); font-size: 0.84rem; letter-spacing: 0.08em; text-transform: uppercase; }
.question .q { font-family: var(--font-serif); font-size: 1.05rem; color: var(--c-navy); margin-bottom: 12px; }
.choices { list-style: none; padding: 0; margin: 0 0 14px; display: grid; gap: 6px; counter-reset: choice; }
.choices li { padding: 10px 14px; background: var(--c-bg); border-radius: 8px; font-family: var(--font-serif); position: relative; padding-left: 44px; counter-increment: choice; }
.choices li::before {
  content: counter(choice, upper-alpha);
  position: absolute; left: 12px; top: 50%; transform: translateY(-50%);
  display: inline-grid; place-items: center; width: 24px; height: 24px;
  background: var(--c-navy); color: #fff; border-radius: 50%; font-family: var(--font-sans); font-weight: 700; font-size: 0.78rem;
}
details.answer summary { cursor: pointer; font-family: var(--font-sans); font-weight: 700; color: var(--c-amber-deep); padding: 6px 0; }
details.answer summary:hover { color: var(--c-navy); }
.answer-body { padding-top: 10px; color: var(--c-ink-soft); }
.answer-body strong { color: var(--c-navy); }

/* ---------- Tables (exam structure / unit weights) ---------- */
.data-table { width: 100%; border-collapse: collapse; margin: 14px 0 22px; font-family: var(--font-sans); font-size: 0.93rem; }
.data-table th, .data-table td { text-align: left; padding: 12px 14px; border-bottom: 1px solid var(--c-line); }
.data-table th { background: var(--c-cream); color: var(--c-navy); font-weight: 700; border-bottom: 2px solid var(--c-amber); }
.data-table tr:hover td { background: var(--c-bg); }

/* ---------- Key ideas / callouts ---------- */
.key-ideas {
  background: linear-gradient(180deg, var(--c-amber-soft) 0%, #fff 100%);
  border: 1px solid #ecd99a; border-left: 4px solid var(--c-amber);
  border-radius: var(--radius); padding: 18px 22px; margin: 22px 0;
}
.key-ideas h3 { margin: 0 0 8px; color: var(--c-navy); font-family: var(--font-sans); font-weight: 700; }
.key-ideas ul { margin: 0; padding-left: 22px; }
.callout { background: var(--c-cream); border-left: 4px solid var(--c-navy); padding: 14px 20px; border-radius: 8px; margin: 18px 0; font-family: var(--font-serif); }
.callout strong { color: var(--c-navy); }

/* ---------- Resource list ---------- */
.resource-list { list-style: none; padding: 0; margin: 0; display: grid; gap: 12px; }
.resource-list li {
  background: var(--c-paper); border: 1px solid var(--c-line); border-left: 4px solid var(--c-amber);
  border-radius: var(--radius); padding: 16px 20px;
}
.resource-list a { font-family: var(--font-sans); font-weight: 600; color: var(--c-navy); }
.resource-list .desc { color: var(--c-ink-soft); margin-top: 4px; font-size: 0.95rem; }

/* ---------- Tag / pills ---------- */
.pill {
  display: inline-block; font-family: var(--font-sans); font-weight: 600; font-size: 0.74rem;
  text-transform: uppercase; letter-spacing: 0.08em; padding: 4px 9px; border-radius: 999px;
  background: var(--c-amber-soft); color: var(--c-navy); border: 1px solid #ecd99a; margin-right: 6px;
}
.pill.dark { background: var(--c-navy); color: #fff; border-color: var(--c-navy); }

/* ---------- Course header (per-course AP main) ---------- */
.course-hero {
  background: var(--c-paper); border: 1px solid var(--c-line); border-top: 4px solid var(--c-amber);
  border-radius: var(--radius-lg); padding: 28px 32px; margin-bottom: 28px; box-shadow: var(--shadow-sm);
}
.course-hero .pills { margin-bottom: 10px; }
.course-hero h1 { margin: 0 0 8px; }
.course-hero .lead { margin: 0 0 18px; color: var(--c-ink-soft); }
.course-cta { display: flex; gap: 10px; flex-wrap: wrap; }

.facets { display: grid; grid-template-columns: repeat(auto-fit, minmax(180px, 1fr)); gap: 0; margin-top: 20px; border-top: 1px solid var(--c-line-soft); }
.facet { padding: 16px 20px 0; font-family: var(--font-sans); border-right: 1px solid var(--c-line-soft); }
.facet:last-child { border-right: none; }
.facet .lbl { font-size: 0.74rem; color: var(--c-muted); text-transform: uppercase; letter-spacing: 0.1em; font-weight: 600; }
.facet .val { font-family: var(--font-display); color: var(--c-navy); font-weight: 700; font-size: 1.15rem; margin-top: 4px; display: block; }

/* ---------- FRQ block ---------- */
.frq-block {
  background: var(--c-paper); border: 1px solid var(--c-line); border-left: 4px solid var(--c-navy);
  border-radius: var(--radius); padding: 20px 24px; margin: 20px 0;
}
.frq-block h3 { margin-top: 0; color: var(--c-navy); }
.frq-block .frq-meta { font-family: var(--font-sans); font-size: 0.84rem; color: var(--c-muted); margin-bottom: 6px; text-transform: uppercase; letter-spacing: 0.08em; }

/* ---------- Footer ---------- */
.site-footer { background: var(--c-navy-deep); color: #cfd6e8; margin-top: 80px; padding: 48px 0 24px; font-family: var(--font-sans); }
.site-footer .brand { color: #fff; }
.site-footer .brand-mark { background: var(--c-amber); color: var(--c-navy); }
.site-footer .brand-name { color: #fff; }
.footer-grid { display: grid; grid-template-columns: 1.6fr repeat(3, 1fr); gap: 36px; margin-bottom: 32px; }
@media (max-width: 880px) { .footer-grid { grid-template-columns: 1fr 1fr; gap: 28px; } }
.site-footer h4 { color: #fff; margin: 0 0 14px; font-size: 0.82rem; text-transform: uppercase; letter-spacing: 0.12em; font-weight: 700; }
.site-footer .bare li { margin-bottom: 8px; }
.site-footer a { color: #cfd6e8; text-decoration: none; border-bottom: 1px solid transparent; }
.site-footer a:hover { color: #fff; border-bottom-color: var(--c-amber); }
.site-footer p { margin: 0 0 8px; color: #cfd6e8; }
.footer-bottom { border-top: 1px solid #1d2c4d; padding-top: 18px; font-size: 0.86rem; color: #92a0c2; }
.footer-bottom p { margin: 4px 0; color: inherit; }

.muted { color: var(--c-muted); }
.small { font-size: 0.84rem; }