Skeleton
A pulsing block at whatever width and height you give it. It is decorative and needs no ARIA.
The pulse stops under prefers-reduced-motion. Skeletons are for content that is about to arrive; for an action already under way, a spinner says so more honestly.
.hui-skeleton
A pulsing placeholder for content that is still loading.
<div class="hui-skeleton" style="height:1rem;width:60%"></div>