@jaffathecake That is really weird & problematic, IMO. Is there any other case where the browser dynamically injects content in the light DOM?

Are styling hooks for shadow DOM still so bad that can't be adjusted?

Alternatively, again borrowing from SVG convention: The cloned element within a <use> brings with it style rules from its original context. For the selectedoption use case, you could then add a pseudoclass or host rule that matches the original element only in the cloned context.