> At quick glance, it looks like they're still using the same CSS that was made public ~13 years ago:

It has been changed since then for sure though. A couple of years ago the mobile experience was way worse than what it is today, so something has clearly changed. I think also some infamous "non-wrapping inline code" bug in the CSS was fixed, but can't remember if that was months, years or decades ago.

On another note, they're very receptive to emails, and if you have specific things you want fixed, and maybe even ideas on how to do in a good and proper way, you can email them (hn@ycombinator.com) and they'll respond relatively fast, either with a "thanks, good idea" or "probably not, here's why". That has been my experience at least.