/* Sticky site header — loaded on every page, both bundles. No ancestor of
establishes a containing block (no overflow/transform), so position:sticky works without switching to fixed + body padding. */ .site-header { position: sticky; top: 0; z-index: 1030; /* above the page's own overlays and animations */ background: #fff; transition: box-shadow .18s ease; } /* JS adds .is-stuck to once the page has scrolled. */ .is-stuck .site-header { box-shadow: 0 1px 12px rgba(0, 0, 0, .18); } /* In-page anchors must not land under the pinned bar. */ :target, [id] { scroll-margin-top: 88px; } /* The mobile drop-down hangs off the header, so it travels with it. */ .mainnav-mobile { z-index: 1029; } @media (prefers-reduced-motion: reduce) { .site-header { transition: none; } }