/* ─── CBTC Author Site — Design tokens & shared styles ─────────────────── */
:root {
  /* Palette derived from book covers */
  --navy:      #0A1628;
  --navy-deep: #07101D;
  --navy-mid:  #1B2D4A;
  --cyan:      #4A9EBF;
  --cyan-dim:  rgba(74, 158, 191, 0.35);
  --amber:     #D4A84B;
  --amber-soft: rgba(212, 168, 75, 0.18);
  --ink:       #EAF2F7;
  --ink-dim:   rgba(234, 242, 247, 0.62);
  --rule:      rgba(234, 242, 247, 0.16);

  --paper:     #F4EFE6;
  --paper-2:   #EAE2D2;
  --char:      #1A1A1A;
  --char-dim:  rgba(26, 26, 26, 0.62);
  --char-rule: rgba(26, 26, 26, 0.14);

  --serif: "Source Serif 4", "Crimson Pro", Georgia, serif;
  --sans:  "IBM Plex Sans", -apple-system, system-ui, sans-serif;
  --mono:  "IBM Plex Mono", ui-monospace, Menlo, monospace;

  --container: 1280px;
  --gutter: 32px;
}

* { box-sizing: border-box; }
html, body { margin: 0; padding: 0; }
body {
  font-family: var(--sans);
  font-size: 16px;
  line-height: 1.5;
  background: var(--paper);
  color: var(--char);
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}
img { max-width: 100%; display: block; }
a { color: inherit; text-decoration: none; }
button { font: inherit; cursor: pointer; }

/* ─── Universal nav ─────────────────────────────────────────────────────── */
.site-nav {
  position: sticky; top: 0; z-index: 50;
  background: var(--paper);
  border-bottom: 1px solid var(--char-rule);
  backdrop-filter: saturate(180%) blur(8px);
}
.site-nav-inner {
  max-width: var(--container);
  margin: 0 auto;
  padding: 18px var(--gutter);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 32px;
}
.site-nav-brand {
  font-family: var(--mono);
  font-size: 12px;
  letter-spacing: 2px;
  text-transform: uppercase;
  display: flex; align-items: center; gap: 10px;
  color: var(--char);
}
.site-nav-brand .dot {
  width: 8px; height: 8px; background: var(--amber); display: inline-block;
}
.site-nav-links {
  display: flex; gap: 28px;
  font-family: var(--mono);
  font-size: 12px;
  letter-spacing: 1.4px;
  text-transform: uppercase;
}
.site-nav-links a {
  color: var(--char-dim);
  padding-bottom: 3px;
  border-bottom: 1px solid transparent;
  transition: color .15s, border-color .15s;
}
.site-nav-links a:hover { color: var(--char); border-bottom-color: var(--amber); }
.site-nav-links a.active { color: var(--char); border-bottom-color: var(--amber); }
.site-nav-cta {
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 1.6px;
  text-transform: uppercase;
  background: var(--navy);
  color: var(--ink);
  padding: 10px 18px;
  display: inline-flex; align-items: center; gap: 8px;
}
.site-nav-cta:hover { background: var(--char); }

/* ─── Footer ────────────────────────────────────────────────────────────── */
.site-foot {
  background: var(--navy);
  color: var(--ink);
  margin-top: 120px;
}
.site-foot-inner {
  max-width: var(--container);
  margin: 0 auto;
  padding: 80px var(--gutter) 40px;
  display: grid;
  grid-template-columns: 2fr 1fr 1fr 1fr;
  gap: 56px;
}
.site-foot h4 {
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 2px;
  text-transform: uppercase;
  color: var(--amber);
  margin: 0 0 18px;
  font-weight: 500;
}
.site-foot a { color: var(--ink-dim); display: block; padding: 4px 0; font-size: 14px; }
.site-foot a:hover { color: var(--ink); }
.site-foot-mark {
  font-family: var(--serif);
  font-size: 28px;
  font-weight: 400;
  line-height: 1.15;
  letter-spacing: -0.5px;
  margin-bottom: 14px;
}
.site-foot-mark em { color: var(--amber); font-style: normal; }
.site-foot-bottom {
  border-top: 1px solid var(--rule);
  max-width: var(--container);
  margin: 0 auto;
  padding: 24px var(--gutter);
  display: flex; justify-content: space-between;
  font-family: var(--mono); font-size: 11px;
  letter-spacing: 1.4px; text-transform: uppercase;
  color: var(--ink-dim);
}

/* ─── Reusable bits ─────────────────────────────────────────────────────── */
.kicker {
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 2.4px;
  text-transform: uppercase;
  color: var(--char-dim);
  display: inline-flex; align-items: center; gap: 10px;
}
.kicker::before {
  content: ""; width: 24px; height: 1px; background: var(--amber);
}
.kicker.on-dark { color: var(--ink-dim); }
.rule { height: 1px; background: var(--char-rule); border: 0; margin: 0; }
.rule.on-dark { background: var(--rule); }

.btn {
  display: inline-flex; align-items: center; gap: 10px;
  padding: 14px 22px;
  font-family: var(--mono);
  font-size: 12px;
  letter-spacing: 1.8px;
  text-transform: uppercase;
  border: 1px solid currentColor;
  transition: background .15s, color .15s;
}
.btn-primary { background: var(--navy); color: var(--ink); border-color: var(--navy); }
.btn-primary:hover { background: var(--amber); color: var(--navy); border-color: var(--amber); }
.btn-ghost { background: transparent; color: var(--char); }
.btn-ghost:hover { background: var(--char); color: var(--paper); }
.btn-ghost.on-dark { color: var(--ink); }
.btn-ghost.on-dark:hover { background: var(--ink); color: var(--navy); }

/* ─── 3D book ───────────────────────────────────────────────────────────── */
.book3d {
  perspective: 2400px;
  display: inline-block;
}
.book3d-inner {
  position: relative;
  transform-style: preserve-3d;
  transition: transform .8s cubic-bezier(.2,.7,.2,1);
  transform: rotateY(-28deg) rotateX(4deg);
}
.book3d:hover .book3d-inner { transform: rotateY(-12deg) rotateX(2deg); }
.book3d.flipping .book3d-inner { transform: rotateY(-152deg) rotateX(2deg); }
.book3d-face {
  position: absolute; top: 0; left: 0;
  width: 100%; height: 100%;
  background-size: cover;
  background-position: center;
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;
}
.book3d-front  { transform: translateZ(var(--spine, 24px)); }
.book3d-back   { transform: translateZ(calc(var(--spine, 24px) * -1)) rotateY(180deg); }
.book3d-spine-l {
  width: calc(var(--spine, 24px) * 2);
  left: calc(var(--spine, 24px) * -1);
  transform: rotateY(-90deg);
  transform-origin: right center;
}
.book3d-spine-r {
  width: calc(var(--spine, 24px) * 2);
  right: calc(var(--spine, 24px) * -1);
  transform: rotateY(90deg);
  transform-origin: left center;
}
.book3d-top, .book3d-bottom {
  height: calc(var(--spine, 24px) * 2);
  width: 100%;
  background: repeating-linear-gradient(90deg, #f4eede 0 2px, #e6dcc4 2px 3px);
}
.book3d-top {
  top: calc(var(--spine, 24px) * -1);
  transform: rotateX(90deg);
  transform-origin: center bottom;
}
.book3d-bottom {
  bottom: calc(var(--spine, 24px) * -1);
  transform: rotateX(-90deg);
  transform-origin: center top;
}

/* ─── Utility containers ────────────────────────────────────────────────── */
.container {
  max-width: var(--container);
  margin: 0 auto;
  padding: 0 var(--gutter);
}
.section { padding: 96px 0; }
.section-tight { padding: 64px 0; }

/* Responsive */
@media (max-width: 900px) {
  .site-nav-links { display: none; }
  .site-foot-inner { grid-template-columns: 1fr 1fr; }
  .section { padding: 64px 0; }
}