If you're on one of the betas for about-to-be-released apple OS’s, there's a new describe an extension functionality and building a dark mode for HN is exactly what I just used it to do. Super easy, and synced across all my devices.

I know this sounds like an ad, but I was pretty impressed with it

Great idea! I tried this just after reading your comment, 20s later I had a working extension that does exactly this for HN.

Thank you!