Dark mode

[vnl]

Well, I believe the title says it all. A feature request to implement dark mode.

I have started the code so I should be able to get a PR for this.

[vnl]

Still, a few things to work on.

• The buttons look odd - need spaces
• In light mode, the navbar is light with black text. I want to get it back to the original.
• Calendar also adjusts to dark mode.

[pbogre]

Thanks a lot for the issue and contribution! I'd be willing to discuss this more thoroughly in the PR. Feel free to open the PR even if it's not finished yet (as a draft), so we can discuss the technicalities in there rather then the issue.

[vnl]

Done PR created.