According to the @CSS documentation (
https://conductance.io/reference#mho:surface::Style), it seems that you can use // as a comment, like in JS.
This mostly sorta works, but it's not quite right, because it seems that the parser is in fact parsing the content inside //. This is easy to demonstrate:
@CSS(`// '`)
So, either // should be made into a proper comment (and behave the same way as in JS), or the documentation should be changed to use /* */ instead.