I've been toying with the idea of a Dark Mode/theme for Community.. but then stumbled across this Chrome Extension which does a pretty good job on any site, without the need for any coding

 

https://chrome.google.com/webstore/detail/dark-reader/eimadpbcbfnmbkopoojfekhnkhdbieeh

 

 

It's not perfect, but in general it works well & is worth a look if you want to give your eyes a rest.