My Hacker News extension [1] re-applies the colours from HN's news.css (including the mistakes in it ^_^) using CSS variables [2] to make it themeable, and adds a default dark mode with an OLED variant, and a way to apply your own theme CSS.

Personally I'm using an HN version of Twitter's Dim theme [3]

[1] https://soitis.dev/comments-owl-for-hacker-news

[2] https://github.com/insin/comments-owl-for-hacker-news/blob/m...

[3] https://imgur.com/a/comments-owl-hacker-news-dark-modes-iFSk...