I solved that I could not see a background image at all.
But this was only when the Diagram had a board rim; apparently part of the rim was growing out of proportion, and covered the entire board.
I now solved the other problem too, though. I had forgotten to write 'document.' before the 'getElementById' when I assigned the new background to style.backgroundImage. In the Diagram below the background switch now works for me:
I solved that I could not see a background image at all. But this was only when the Diagram had a board rim; apparently part of the rim was growing out of proportion, and covered the entire board.
I now solved the other problem too, though. I had forgotten to write 'document.' before the 'getElementById' when I assigned the new background to style.backgroundImage. In the Diagram below the background switch now works for me:
Unsolved (but unrelated) mystery is why after a short time most of the green background disappears. I don't know if others experience that too.