.site-nav {
  position: sticky;
  top: 0;
  z-index: 50;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--space-2) var(--space-3);
  background: transparent;
  transition: background var(--transition-fast), box-shadow var(--transition-fast);
}

/* No backdrop-filter: a blurred header compositing above the Study Diary
   page's preserve-3d flip layers underneath it is a known trigger for GPU
   layer-blend glitches (flash/flicker) during the flip animation — an
   opaque-enough solid background reads the same without the blur cost. */
.site-nav.is-scrolled {
  background: rgba(245, 244, 240, 0.9);
  box-shadow: 0 1px 0 rgba(0, 0, 0, 0.05);
}

.site-nav__brand {
  font-family: var(--font-display);
  font-size: 1.1rem;
  color: var(--color-text);
}

.site-nav__links {
  display: flex;
  gap: var(--space-3);
  list-style: none;
  margin: 0;
  padding: 0;
}

.site-nav__links a {
  color: var(--color-text);
  font-size: 0.95rem;
  letter-spacing: 0.02em;
  padding-bottom: 2px;
  border-bottom: 2px solid transparent;
  transition: border-color var(--transition-fast), color var(--transition-fast);
}

.site-nav__links a:hover,
.site-nav__links a[aria-current="page"] {
  color: var(--color-klein-blue);
  border-bottom-color: var(--color-klein-blue);
}

.site-nav__toggle {
  display: none;
  background: none;
  border: none;
  font-size: 1.2rem;
  cursor: pointer;
}

.site-footer {
  text-align: center;
  padding: var(--space-4) var(--space-3);
  color: var(--color-text-muted);
  font-size: 0.8rem;
}

@media (max-width: 768px) {
  .site-nav__links {
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    flex-direction: column;
    background: var(--color-surface);
    padding: var(--space-2) var(--space-3);
    gap: var(--space-2);
    display: none;
  }

  .site-nav__links.is-open {
    display: flex;
  }

  .site-nav__toggle {
    display: block;
  }
}