Skeleton blocks with a highlight sweeping across them every 1.4 seconds.

The sweep is a pseudo-element translated across the block rather than a moving background-position, so the whole effect stays on the compositor and costs nothing in paint however many skeletons are on screen. The highlight is a three-stop gradient that is transparent at both ends, which is what makes it read as a passing light rather than a moving bar. Blocks are given their own widths so the placeholder has the ragged right edge real text has. Under reduced motion the skeleton stays and only the sweep is removed.