TLDR: Atom has a handful of internally-defined CSS style names such as close and label which end up conflicting with styles generated for the purposes of syntax highlighting.

I reported the issue on the forum, and another person also ran across it:

• http://discuss.atom.io/t/serious-problem-with-css-style-namespace-vis-a-vis-syntax-highlighting/4794
• http://discuss.atom.io/t/assembly-default-label-styles-are-annoying/5667

Is this considered to be a bona fide problem? If so, maybe this package is where at least part of the fix should be.