This is feedback for the website. Please add a dark theme option. For some people, like me who like to study in the night time, staring at a white screen can put a lot of stress to the eyes. I recommend that there be a simple toggle button for a night mode option.
If there is a way to do this, I am not aware.

While in test mode you can click on the gear at the top right to select dark theme options. You are able to select white, black, or sepia.
I hope this feedback is helpful!