Just discovered a fascinating little story in the CSS world.
There was a last minute change of mind about whether container-type: inline-size
(i.e. Container Queries) should create a stacking context or not. As of right now, the CSS spec says yes, but Chrome 129 switched to no. Apparently all browsers (and the spec) will soon be updated to this new behavior, but right now major browsers are not interoperable on this. Article with great demos and CSS-WG issue links.