SVG <use> tag with CSS ::part selector

[Glandos]

I have an edge case with https://codepen.io/glandos/pen/XWzWgbe

In Firefox:

In Chromium-based browser:

The CSS is:

circle {
  fill: red;
}

g *::part(export) {
  fill: blue;
}

The first circle is defined in the group, the other one is via a def/use, so it is drawn within a closed shadow DOM.
Is it covered in any spec right now? It's hard to find what should be applied. Of course, I'd like to think that Firefox does the right thing because that's what I want to do 😄

[trusktr]

For such issues, it is also a good idea to file it here:

https://github.com/webcompat/web-bugs

The people there will help ensure the differences are catalogued and reported to each browser bug tracker.

[Glandos]

Watch https://bugs.chromium.org/p/chromium/issues/detail?id=1479000 (and parent https://bugs.chromium.org/p/chromium/issues/detail?id=785246) for resolution.