[fullscreen] Styles of former fullscreen elements (#18)

In the current spec, the `:fullscreen` pseudo-class only applies to the current fullscreen element. It means, if the document has been in fullscreen, and the content requests fullscreen on another element, the previous fullscreen element would still in the top layer, but no longer have fullscreen styles applied.

This seems broken to me. I think an element should have either the full set of fullscreen styles as well as top layer styles, or none of them.

It seems to me there are three ways to solve this:

1. apply `:fullscreen` to all elements with fullscreen flag set instead of only the topmost one
2. add another pseudo-class for selecting elements in the top layer with fullscreen flag set
3. restore the fullscreen element stack concept, and only put the topmost element to the top layer

Personally, I prefer (3), because it seems to need the least change to our current impl, and is also most compatible with the current behavior. I don't really believe (1) or (2) could break any real website, though.

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Reply to this email directly or view it on GitHub:
https://github.com/whatwg/fullscreen/issues/18