Bugzilla – Bug 15196
[Shadow]: Specify a way of explicitly allowing some styles reaching into shadow DOM subtrees
Last modified: 2012-10-23 21:18:43 UTC
For the moment, I intend to punt this completely and use CSS Variables to provide specific styling hooks in the shadow DOM, but it's still worth looking again at the "pseudo".
Developers requested that on many occasions. CSS Variables isn't enough.