> no cookie popups, no "subscribe to our newsletter" slide-ins, no phenomenon where the content loads but then a second later the page resets and re-loads the content again (probably with more ads or something)
to fix rendering layout using tables and cell width to render comment levels.
Just a few lines of CSS and Arc really. That would be a big overhaul only because HN is very small, but not that big in absolute.
.comment { font-size: 14pt; } .comhead { font-size: 12pt; }
I set this up many years ago and have not had to touch it since.
But I also find it too small on my mobile, and increasing the font size doesn't improve things, just makes it necessary to scroll sideways to read the comments.
Overall the font size settings on HN are crap. I really wish @dang would listen to the frequent complaints and fix them.
Anyway, the "errors" that OP mentions are simply just deprecated attribute styling and like, one or two instances of center tags. Hardly breaking anybody's back to continue supporting those.
Almost all of the warning and errors are related to using obsolete Element attributes and invalid <table> definitions. Those shouldn't need any larger rework to clean up.
I don't say this trying to imply that HN needs to fix these or are being lazy in not doing it. YC has priorities and provide HN for free. It's totally up to them whether fixes are worth it, I just wouldn't expect it to be a huge lift.