[mediaqueries-5][css-conditional-5][css-mixins-1] Order dependent rules and adopted stylesheets

[andruud]

Adopted stylesheets are appended at the end of the list of stylesheets. This means that names defined by order dependent rules (e.g. @mixin, @custom-media) won't be visible in the regular stylesheets at all, which doesn't seem ideal.

What can we do about this? Reconsider order dependence? Add a way to prepend sheets? Accept this limitation, and hope that @sheet saves us (#11509)?