Did you know GitLab has themes? https://www.dropbox.com/s/p6b8yupsw4opsuu/Screenshot%202017-...
The point was that while the code frame has a dark theme, the webpage around it still blasts you with light, which causes the strain. GitLab doesn't support themes across the whole website (yet?)
The dark theme I use is Dracula[1], it's a really beautiful theme and if there was a way to view GitLab using it it'd be incredible.
[1]: https://draculatheme.com/vim/