Add dark mode support

[gprasanth]

Would be great to include dark mode support for this.

Should be trivial to implement, and can be implemented as a toggle at the top right of the screen and further, can respect the system dark mode setting and switch mode automatically on page load.

The feature itself has already been done pretty well at loads of places, just needs the plumbing here.

[Sebring]

Should be trivial to implement

Im sure PR's are welcomed ;)