You can also use the Dark Reader browser extension [0], an open-source extension for Chromium and Firefox that works on most websites (including Hacker News) in the dynamic mode, restyling the page to a dark theme!
When I can access something in the browser rather than only via native apps, I rely heavily on Dark Reader, Midnight Lizard, and Page Shadow. Love all three to death
[0]: https://darkreader.org/