SVGs \ Diagram colors being influenced by browser themes

[LogicalDestruction]

Issue Description

I'm not sure when this happened as I haven't created a diagram in a while. But recently I made a diagram and for some reason it showed up all black. I finally figured out that the SVGs created by Diagrams are now taking on the theme configured in the browser. Older diagrams in our wiki show up as expected. If I use another browser without a theme the dark theme doesn't show up in the images so I'm pretty sure this is something to do with how the images are created?

I'll try to paste a image \ screenshot of an example. The top image is from diagram from some time ago and the bottom was made recently. I've run a few updates to both the wiki and diagrams since the 1st image but you can see what I'm talking about above.

thanks!

[annda]

I am not sure since when, but now diagrams.net is per default exporting SVG diagrams like this. The same color change will happen on older diagrams too when we edit them.

Some people welcome this change (see #60). But this is not what most users are expecting. We should probably adjust our code to handle this change.

There is a PR #55 which adds a configuration option to set the theme manually. @splitbrain we need to decide what needs to be done.