define CSS exports in package.json

I'm not sure if you want to export the src or dist folders, or both? I intend to use the src to compile from, giving project owners more control over any post-processing, so that's what's in this MR. Happy to take direction of course.

I tested this out locally and it resolved the issue, built just fine. I have *no idea* how I could make any kind of automated test for this.

Automatically closed - issue fixed for 2 weeks with no activity.