.site-header::before {
  content: ""; position: absolute; inset: 0; z-index: -1; opacity: 0;
  background: rgba(22, 21, 26, 0.72);
  -webkit-backdrop-filter: blur(18px) saturate(1.4); backdrop-filter: blur(18px) saturate(1.4);
  border-bottom: 1px solid rgba(255, 255, 255, 0.06);
  transition: opacity 0.3s ease;
}
.site-header.is-solid::before { opacity: 1; }
main section[id] { scroll-margin-top: 5rem; }