This is incidental. The current Jupyter CSS needs to be improved - so what? That's not a bug unique to Jupyter, I've seen dozens of other websites with similar problems (some with extremely bare HTML and CSS that was minimal but bad - so the problem is unrelated to complexity, too).

This has nothing to do with the parent comment's topic, which was about using computational notebooks as blog posts, and is in effect "complaining about tangential annoyances—e.g. article or website formats, name collisions, or back-button breakage" - which the guidelines explicitly forbid.