Dark Mode

Among a few minor fixes, this new version solves a theming problem that was reported to me.
I was unable to reproduce it until I have been affected myself after a Windows update, which helped me quickly spot the cause and correct it in my code.

Among a lot of fixes and changes, the most visible changes of this new version are the addition of the popular Dark Mode, and the simplification of the Ribbon menu, into a less space wasting Ribbon.