The CSS spec does not mention it, but you can mimic C-style and/or unix-style line comments in CSS files (with some caveats). Others have written about them before (see in particular, SitePoint’s Web Foundations post covering CSS Comments). The present post examines them in further detail.
“If there are no tests, it does not work,” a former colleague said, who could have added, “whether your code or someone else’s.”
I’m not the first to say it but it needs re-stating: 3rd-party libraries are no guarantee that your code continues to behave as expected.
If one of the duties of your work is making sure you’re not introducing bloat or cruft or inefficiencies or bugs or unexpected behavior, then you’re cutting corners if you don’t have tests, whether you use 3rd-party code or not.