Should they have one? Or should a normal declaration with no encapsulation context not take precedence over a normal declaration with an encapsulation context?
Browsers do not give precedence to a normal declaration in the user or user agent style sheet over a normal declaration in a shadow tree.
When comparing two declarations that are sourced from different encapsulation contexts, then for normal rules the declaration from the outer context wins [...].
I do not think the encapsulation context of the user or user agent style sheet is defined anywhere. I do not know if all declarations must have an encapsulation context:
A document language can provide for blending declarations sourced from different encapsulation contexts [...].
https://drafts.csswg.org/css-cascade-5/#cascade-context
Should they have one? Or should a normal declaration with no encapsulation context not take precedence over a normal declaration with an encapsulation context?
Browsers do not give precedence to a normal declaration in the user or user agent style sheet over a normal declaration in a shadow tree.
I do not think the encapsulation context of the user or user agent style sheet is defined anywhere. I do not know if all declarations must have an encapsulation context:
https://drafts.csswg.org/css-cascade-5/#cascade-context