<noscript> is pretty much a feature of the HTML parser. It disappears. The DOM representation doesn’t include a <noscript> element, so you can’t style it. (This is also why you can’t use <noscript> in the XML syntax of HTML. If you don’t know about the XML syntax, I’ll simplify and say it roughly means what was commonly called XHTML.)
What makes it even less useful is that the absence of the <noscript> content doesn’t mean that your scripts are being executed. If you use something like uMatrix or uBlock Origin to block certain types of scripts, for example, you might find that none of the scripts execute, but that the <noscript> content is also not loaded, because it could have executed some scripts, if the right URLs had been requested. Or perhaps the browser was happy to execute JavaScript, it’s just that it failed to fetch the JavaScript, for whatever reason. (Perhaps you put your JS on a CDN, on a different origin, and it’s down.)
In the end, the .no-js approach is far superior to the use of <noscript>.