[css-cascade-6] Add ability to scope rules from an imported stylesheet

[mozilla-apprentice]

Resolutions were made for csswg-drafts/#7348.

[css-cascade-6] Add ability to scope rules from an imported stylesheet

• RESOLVED: allow full reordering of all the current conditions on @import (MQ, scope, ...)
• RESOLVED: the WG recommends having an attribute to enable @scope on the HTML link element

Discussion.

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