Doesn’t need to be “JSS”, there are plenty of competitors.
For me, the whole point is to use javascript and npm modules to adapt my css at runtime. That way you can have “data-binding” for your css or “reactivity” if you want. On top of that you can get automation of BEM conventions the same as you get them with css modules.

It’s possible there is a more minimal way than jss, but jss seems to be one of the most mature and feature rich to prototype a javascript based workflow.

Once it’s more clear which ways work I can write my own “jss” wrapping the native browser API, e.g.:

document.styleSheets[1].cssRules[0].style.backgroundColor = ‘#f00’