CSJS author here, thanks for the plug! I think CSJS fairly unique in comparison to the numerous alternatives in that it:

1) Can be used without any tooling whatsoever. It's just plain JS.

2) Doesn't reinvent the wheel. You can use regular CSS (normal syntax, pseudo classes, media queries) and regular JS (variables, modules) together, allowing you to use the best of both worlds.

I loved the ideas behind CSS Modules but wasn't sure about the complexity of re-implementing a new module/variable syntax into CSS. Why not just use what is already provided in JavaScript?