I created a userstyle[1] to add "dark mode" to HN, along with some increased text sizes, white space, and line heights to improve legibility:

https://git.gioia.cloud/andrew/gists/src/branch/master/Userstyles/Hacker%20News%20Dark.css

The idea is to maintain the spirit of HN and to just make some modest enhancements[2]. Hope you can use it!

[1] https://github.com/openstyles/stylus

[2] Based on https://github.com/Poorchop/userstyles/tree/master/HackerNews-Dark