A lot of people using Atom might know about the Apex theme, the monochromatic color scheme theme that's inspired from IAWriter. It's a really slick theme. The better version is the Apex Slim theme and that theme just aesthetically pleases the crap out of me and I was using it for a while but I updated Atom recently and the theme wasn't really fitting in well with it. (aka broken, the tabs went haywire, etc)
Instead of creating an issue I just went over, forked it and fixed it while also adding other mods for my usage.
Now this is only built for macOS because it requires, Atom's Custom Title bar feature enabled.
As for others, you can just install the normal Apex-UI and you should be good to go.
Check it out and you can raise issues if you have any.