Comment 8 for bug 1866961

horizon has fixed the issue but unfortunately the fixes are not linked with it. I am summarizing the fixes.
Multiple fixes are involved in the master branch (i.e. ussuri), so fixes in the stable/train branch would be better for the summary.

The related fixes in stable/train are as follows:
- 9813577f7d0137da0e29c7630cffc3e1e1b329f5 (Update pyScss to 1.3.7)
- f26c88721614d1c25bcd26740b8fb20a7a97bd05 (Implement 'selector-append' sass function) which fixes an problem in the material design with pyScss 1.3.5 or later.

They were backported to stable/stein too.

Regarding stable/rocky or older branches, we don't backport them from the following reasons:
- The CI jobs are not broken as they use setuptools<46.
- It is better to avoid requirements change as much as possible.
- stable/rocky and older branches are in the extended maintenance phase so the upstream development team does not focus on them much.