/* GCBoK Navigation */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: oklch(from var(--c-paper, #FBFAF7) l c h / 0.92);
  backdrop-filter: blur(14px);
  -webkit-backdrop-filter: blur(14px);
  border-bottom: 1px solid var(--c-line);
  transition: box-shadow var(--t-smooth);
}
.site-header.scrolled {
  box-shadow: var(--shadow-sm);
}

.nav-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--sp-8);
  height: 60px;
  max-width: var(--maxw);
  margin-inline: auto;
  padding-inline: var(--sp-6);
}

.nav-logo {
  display: flex;
  align-items: center;
  gap: var(--sp-3);
  text-decoration: none;
  flex-shrink: 0;
}
.nav-logo:hover {
  opacity: 0.85;
}

.nav-logo-mark {
  width: 36px;
  height: 36px;
  flex-shrink: 0;
}

.nav-logo-text {
  display: flex;
  flex-direction: column;
  line-height: 1.1;
}
.nav-logo-text .wordmark {
  font-family: var(--ff-display);
  font-size: var(--fs-sm);
  font-weight: 700;
  color: var(--c-ink);
  letter-spacing: -0.01em;
}
.nav-logo-text .sub {
  font-size: var(--fs-xs);
  color: var(--c-muted);
  font-family: var(--ff-mono);
  letter-spacing: 0.03em;
}

.nav-links {
  display: flex;
  align-items: center;
  gap: var(--sp-1);
  list-style: none;
  margin: 0;
}

.nav-links a {
  display: block;
  padding: var(--sp-2) var(--sp-3);
  font-size: var(--fs-sm);
  font-weight: 500;
  color: var(--c-body);
  text-decoration: none;
  border-radius: var(--radius);
  transition: color var(--t-fast), background var(--t-fast);
}
.nav-links a:hover {
  color: var(--c-ink);
  background: var(--c-surface-alt);
}
.nav-links a.active {
  color: var(--c-amber);
}

.nav-actions {
  display: flex;
  align-items: center;
  gap: var(--sp-3);
}

/* Theme toggle */
.theme-toggle {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 36px;
  height: 36px;
  border-radius: var(--radius);
  color: var(--c-muted);
  cursor: pointer;
  background: none;
  border: none;
  transition: color var(--t-fast), background var(--t-fast);
}
.theme-toggle:hover {
  color: var(--c-ink);
  background: var(--c-surface-alt);
}

/* Mobile hamburger */
.nav-hamburger {
  display: none;
  flex-direction: column;
  justify-content: center;
  gap: 5px;
  width: 36px;
  height: 36px;
  cursor: pointer;
  background: none;
  border: none;
  padding: var(--sp-2);
  border-radius: var(--radius);
}
.nav-hamburger span {
  display: block;
  height: 2px;
  background: var(--c-ink);
  border-radius: 2px;
  transition: transform var(--t-smooth), opacity var(--t-smooth);
}
.nav-hamburger.open span:nth-child(1) { transform: translateY(7px) rotate(45deg); }
.nav-hamburger.open span:nth-child(2) { opacity: 0; }
.nav-hamburger.open span:nth-child(3) { transform: translateY(-7px) rotate(-45deg); }

/* Mobile drawer */
.nav-drawer {
  display: none;
  position: fixed;
  top: 60px;
  left: 0;
  right: 0;
  background: var(--c-paper);
  border-bottom: 1px solid var(--c-line);
  padding: var(--sp-4) var(--sp-6) var(--sp-8);
  z-index: 99;
  box-shadow: var(--shadow-lg);
}
.nav-drawer.open {
  display: block;
}
.nav-drawer .drawer-links {
  display: flex;
  flex-direction: column;
  gap: var(--sp-1);
  list-style: none;
  margin-bottom: var(--sp-6);
}
.nav-drawer .drawer-links a {
  display: block;
  padding: var(--sp-3) var(--sp-4);
  font-size: var(--fs-base);
  font-weight: 500;
  color: var(--c-body);
  text-decoration: none;
  border-radius: var(--radius);
  transition: background var(--t-fast), color var(--t-fast);
}
.nav-drawer .drawer-links a:hover {
  background: var(--c-surface-alt);
  color: var(--c-ink);
}

@media (max-width: 768px) {
  .nav-links { display: none; }
  .nav-hamburger { display: flex; }
}