struct LayeredView

A base view with a layer drawn behind it (.underlay { }) or over it (.overlayLayer { }), covering its box and taking no layout space and no input.

Built the way the composed overlay(alignment:) is: the layer is an absolutely positioned Yoga child pinned to all four edges, so the base measures exactly as it did without it. What differs is that the layer is inert — every hit walk passes straight through it — and that it can go under the content as well as over it.

For chrome no single fill describes: a tab whose outline runs along three sides and leaves the fourth open, a highlight over a pane that is about to receive a drop. Give the layer .pct(100) in both axes and it is exactly the base's size.