Skeleton

Loading placeholders — the grey, gently shimmering blocks that hold content’s space until it arrives, so the layout doesn’t jump. Three pieces: Skeleton (one block), SkeletonText (a stack of lines approximating a paragraph), and SkeletonImage (an aspect-ratio tile with a faint picture glyph, for grid cells):

Skeleton(width = "12rem", height = "1.25rem")
Skeleton(width = "3rem", height = "3rem", circle = true)   // an avatar

SkeletonText(lines = 3)                 // last line shortened, reads as a paragraph
SkeletonImage(ratio = "16/10")          // reserves a gallery cell

// The canonical "loading tile":
if loaded then ImageCard(src = url, ratio = "16/10")
else SkeletonImage(ratio = "16/10")

Every block takes animated (default true, toggles the shimmer) and rounded; they’re purely decorative (aria-hidden), so assistive tech announces the eventual content, not the placeholder. The shimmer is the one skin-dependent piece (SalleSkin sweeps a sheen, DaisySkin pulses). When the fraction of work is known, reach for Progress instead.