Button styles leaking to editor UI

[simison]

Regular simple site, using Hever theme, Firefox, while proxied, many buttons seem to be visually broken.

Image block, buttons look suspiciously round-cornered and hover state is black:

Social icons block is busted, here are "pills" and "only logos" styles chosen from the sidebar — the blue background probably shouldn't be here and these should be circles:

Classic block buttons:

[WunderBart]

It seems to be theme related. On Blank Canvas it all looks good. I can see that it's broken for i.e. Mayland:

Blank Canvas	Mayland

[simison]

👍 Twenty Twenty One theme worked.

👎 Shawburn theme broken:

[jffng]

This should be resolved since Automattic/themes#3326 was merged + deployed, let me know if you are still encountering issues. Thanks!