Let's build a Perfect CSS Framework

This is an experiment I am doing to build a theoretically perfect CSS framework for teams. Here is how it goes:

1. You comment on this discussion with a problem/issue we currently face with writing CSS (with vanilla CSS or any library).
2. I'll reply (or anyone of you can too) with what can be the probable solutions to that issue.
3. In the end, we collect all those suggested solutions to build or search that "Perfect CSS Framework".

Sounds good? I'll start.