Investigate changing the background color with the color-scheme preference

[flxzt]

As pointed out before, it might be nice to have a changing background color along with color-scheme changes.

To make it work, there are some issues that need to be considered and dealt with:

• we generally don't want to change "foreground" / user content colors, as that would break what the user intended to create.
• changing the background while editing a document might create issues with contrast, especially when using low contrast colors / black-on-black, white-on-white.

Apple note's approach seems to solve this by changing the content colors brightnesses / inverting black-white, see:
https://gfycat.com/informalthoroughdairycow
Off the top of my head there would still be some questions regarding this approach, e.g. what about light-grey / dark-grey colors, would we need to have a contrast-check to trigger color brightness inversions? Maybe we could look into the contrast app and see how they check for that.

opening this to gather ideas for solutions.