[...]
Well, just saying: When you ensure proper lighting in your rooms and do not increase your screen brightness to maximum, then you won't "burn your eyes" given white background. 
Having said that - I know what you mean and rest assured that it'll come at some point. Work is and has been going on for some time, however, a lot of code needs adaptation for fully working theme support. This is likely the reason for why dark mode has also been rejected by the original AdminLTE project.
I wanted to bring user-theming to Pi-hole for a long time and have been working on this every now and then. An issue it that none of the code contributors is a designer (at least not that I'm aware of), however, advice from one would certainly not hurt the overall process. It will be a notable effort to make all the colors definable externally. However, when we reach this point, then colors would need to get picked.
Our current plan is to implement theming support maybe for v5.1. We will likely provide a light and a dark default theme in the beginning. We'll see how things evolve from there. All I can say is that this feature is being and has been worked on for some time.
I just squashed and pushed what I have so far (incomplete!), so if you want to try it (and if you are on the v5.0 beta), run
pihole checkout web new/dark
Make sure to flush your browser cache after running this command. There is currently no theme selector implemented so I hard-coded the dark theme for demonstration.
