support dark mode

[bblfish]

I have been drawing quite a lot of diagrams for issue 1248 of VC Data Model, and in the process developed a trick to make them work in night mode.
If you have OmniGraffle you could adapt that work by chcking it out here https://github.com/co-operating-systems/PhD/tree/main/Logic/VC/model2/

[phochste]

I would love to but I have no clue yet how to change the images when darkmode is active. The images were made in diagrams.net and are SVG files.

[bblfish]

I don't know how to do it there.
In Omnigraffle, I made the lines larger with two lines and a white inside, put a very thick white shadow underneath them, and make the picture transparent with translucent surfaces. It did not work so well with SVG output last I tried because of font problems...