Cool premise, but it locks itself up when I try to change the settings.
The only time I managed to click on something the dropdown menu appeared on the bottom of the page...

EDIT:
I use windows 10 pro, 64bit
Firefox 57 (quantum, 64)

I am guessing it has to do something with my browser being the recently updated version.

In the settings I can now at least change the colours ( it somehow allows me to do that since then) but when I try to click the + button next to day and night mode (or light and darK?) it locks up the page.