Styling for replaced element when a ShadowRoot is attached has a problem. Basically the host element has various styles. We want to reset such styles when an Author Shadow DOM is added, since we want the host element to behave like just a div. It seems good to have a pseudo class to be enabled when the replaced element is 'really' replaced, which means there is an inner special element in the User Agent Shadow DOM in replaced elements.
Created attachment 159024 [details] WIP
Replaced elements don't support a shadow root in V1 API so this is irrelevant now.