fix Overview on dark bg

[nim65s]

Hi,

When github is set on the dark theme, the Overview fig on the README is impossible to read:

A quick fix is to add some colored rectangles behind the black text on transparent background.

[badaix]

Thanks, I think the clean solution is to use two different images, one for light and one for dark mode, as described here:
https://docs.github.com/en/get-started/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax#specifying-the-theme-an-image-is-shown-to

[nim65s]

Sure, this could be a better solution than the quickfix I made. But I have no idea how to choose the colors. Here is a render of my solution, for reference.

What would you change for the dark mode ?