In #11926, we've agreed to add a new view transition pseudo element: view-transition-group-children which copies the border-width property. In #12357 I'm also proposing that we capture border-radius and corner-shape.

Currently we capture these from the "old" element. If the "new" element differs from that, then it can look a bit awkward

In Chrome Canary with experimental web platform features enabled:
https://codepen.io/bramus/full/YPXOXra

Thanks to @bramus for the demo

The proposal here is to follow the pattern we use for group captures: store the "old" element values in a from keyframe, and always update computed style to the "new" values. Also add a keyframe animation on the group-children pseudo that uses the from keyframe.

/cc @noamr