dart-sass import is deprecated

[ufuruya]

https://sass-lang.com/documentation/breaking-changes/import/

https://sass-lang.com/blog/import-is-deprecated/

We’re deprecating both Sass @import rules and global built-in functions now that the module system (@use and @forward rules) has been available for several years.

[nickcharlton]

I expect that this will cease to be a problem once we've made more progress with #2755, either in that PR or in a follow up that gradually gets rid of our use of Sass.

But it's worth keeping this open until we've actually full resolved it. Thanks for opening it!