A long time ago @zcorpan wrote a great set of tests to determine whether features used the URL parser with a non-UTF-8 encoding. As you might expect, there is no interoperability:

https://wpt.fyi/results/html/infrastructure/urls/resolving-urls/query-encoding/windows-1252.html%3Finclude%3Dcss

Everyone seems to agree that @import uses UTF-8, but CSS values depend on the stylesheet encoding in Chromium and WebKit. I wanted to double check with the WG that this is intentional and everyone is on board with aligning with the standard or if this is something that should be changed.