How to use Linaria with custom elements and ShadowDOM / ShadowRoots?

First let me say, this is a nice project!

I'd like to make custom elements, and to give their content styling inside ShadowRoots.

I could possibly `@import` the URL of the output CSS file in every root's ``, but then this would load all styles of every element in each shadow root.

Another thing is, how can we code the custom elements in a way that they do not know what the output URL is?

What about custom elements that will be published as a package for anyone to use? How would the custom elements know the URL to `@import` inside their `<style>` tags?

Any recommendation on how to handle ShadowDOM with Linaria?