There's a new feature of Shadow DOM, specified in the latest Working Draft: reset-style-inheritance flag for insertion points.

It does the same thing as the namesake flag for your shadow DOM subtree: resets all styles to initial style.

Think of it as nice "CSS reset" switch that you can flip any <content> and <shadow> element and make sure that the styles from the shadow aren't inherited by the elements, distributed into those insertion points.
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