How to apply common CSS styles to many Shadow Roots at once?

Question

Consider, I have few elements which use Shadow DOM to hide their internal div-soup and layout.

Even tough they are different, they share the same CSS style sheet, as

Answer 1

UPDATE: 2019 - Use Constructable stylesheets

As of 2019, Constructable stylesheets is the approach to apply stylesheets to shadow DOM and web components in general. Read more about it here.

Previous answer:

You can use an import CSS rule at the first line of a ...

Then import the