[css-view-transitions-2] Copying border shape properties to view-transition-group-children

[vmpstr]

In #11926, we've agreed to add a new view transition pseudo element: view-transition-group-children which copies the border-width property and makes a transparent border. It works well for basic cases:

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

However, if the shape of border is sufficiently different then we end up with clipping artifacts:
https://codepen.io/bramus/full/azOaOLJ

Thanks to @bramus for the demos

The proposal here is to copy more! Specifically, border-radius and corner-shape. I'm open to more features, but also would like to leave this open to all border shape affecting properties

/cc @noamr

[noamr]

Wasn't the idea that the author copies this by themselves?

[bramus]

border-radius seems like a common enough use-case to tackle, so perhaps we should?

Sure authors can copy it manually (see demo 2, with the workaround checkbox ticked) but it becomes tricky when using border-radii with units like em.

[vmpstr]

Yeah I'm not sure this goes beyond border-radius and corner-shape. Authors should be able to easily do this, but since we're already copying border-width, leaving this up to the authors seems a bit like a half-solution