demo · v142

::view-transition position absolute

A tile inside a positioned frame uses view-transition-name. Press "swap" to move it from left to right with a transition. In Chrome 142+ the pseudo tree is positioned absolutely against the snapshot containing block, so the tile slides correctly even though the frame is not the viewport.

positioned frame (containing block)
A
document.startViewTransition
—
current tile side
left

relevant API

/* Tile inside a positioned ancestor */
.tile { view-transition-name: vt-tile2; }

/* In Chrome 142+, ::view-transition is position: absolute and
   resolves against the snapshot containing block, not the viewport. */

see also