{# @description Wraps any background and scrolls it more slowly than the page, so it reads as further away. Stays still where the browser cannot do it. #}
{# @prop speed:number | default:"0.8" | description:"How fast the layer scrolls against the page. 1 moves with the page, 0.5 at half its speed, 0 not at all." #}
{# @prop class:text | description:"Extra classes on the layer" #}
{# @slot One or more backgrounds — What moves. Two of these at different speeds read as two distances. #}
{% comment %}
`overflow-clip`, never `overflow-hidden`: a scroll container between the layer
and the page stops it moving (docs/adr/0004-moving-backgrounds-are-css-only.md).
{% endcomment %}