I added the “Noir” extension to mobile Safari, now I automatically get dark mode on all websites including Hacker News.
I’m surprised by how may don’t have a dark mode though. I decided to do it for my blog despite not really using it myself, and ended up sticking with it on. Still getting blasted in the face by eggshell white everywhere I click.
"Dark Reader" does the same thing on desktop Firefox/Chrome/etc. (& mobile Firefox, maybe also available on mobile Safari?).