Design templates/libraries/etc?

When I’m working on my JS, I tend to throw it into very basic HTML/CSS pages, with the result being that it looks very unimpressive. Sometimes I just want to work on the JS and not mess with the rest of it. Yet in these cases, it looks awful.

I’m wondering what most people do in this situation?

I guess I’m looking for a quick-and-dirty solution, so I can spin up my programs and not have to deal with the aesthetics. In the past, I’ve used Material Design Lite, and another thing I played with yesterday is 90.css.

Does anyone have any suggestions for other quick solutions?