I tried it as a little preview window for writing my blog, which is (in my opinion) very basic HTML and CSS. Whole page rendered wrong, though I admit I didn't bother to find out why. Give it a shot, but keep your expectations low.
If you have a basic site that doesn't work you can open an issue on the repo. If you have some relatively simple site, its useful for the team to know what features that people are using are broken.