In my book, new "baseline" CSS features that handle common design tasks count as simpler (and more user-friendly) than involving JavaScript to set them up, even if it's "vanilla" JS. The user's browser should as much as possible be treating my content as data rather than code and just doing fancy rendering on it, as long as I'm not explicitly trying to show the user a cool program. The browser may be huge, but it's only one thing that has to be huge for the benefit of every site.

(I have much the same instinct about the UNIX philosophy. Bash is not too big. Shell programs should be even bigger so that query programs can be smaller — because otherwise they grow huge lists of options that largely overlap, for things like table formatting, and provide an inconsistent UX.)