There was a bug there; when the auto-generated buttons were used to switch, I assigned the plain URL to style.backroundImage. While it has to be wrapped in 'url(...)'.
I corrected that now, and tried to test it. But I cannot even get a board background to work without any switch buttons. The Diagram in the Comment I am now replying to should use a board background. But instead the board shows up all greyish, like the Comments background color. Even though I set the background color of the <div> that contains the Diagram definition (which will get to contain the container <div> of the board as one of its daughters) to green, the green doesn't shine through.
(I get some sick behavior there too; sometimes the area of the Diagram is all green, as I expect, but then, after a few second, usually at the same time the ads appear, most of the green diappears, and only a tiny bit between the buttons is left.)
It seems that something is not transparent, and that also seems to cover the background image of the board. Any background color I specify for the container <div> also doesn't become visible. So I suppose it is the grid-item <div> elements (i.e. the board squares) that fail to become transparent even when Display assigns an empty string to their style.backgroundColor attribute. When the squares are <td> elements in a table I did not have that problem.
Although the test Diagram there has buttons, the problem already occurs before any of the buttons is pressed, on first parsing of the Diagram. The set lines that define the buttons thus cannot be the problem, these just cause some lines in the definition to be skipped on parsing. And indeed I verified that the behavior remains the same when I delete all these lines.
[Edit] The background (color or image) of the container <div> does not seem to be covered by the background of its daughter items. I can force the latter to a semi-transparent color by using 8-digit color codes for their background, like #FF000080. That gives a pinkish board, showing that the color is indeed used, and that something nearly white shines through. Even though the background color of the container is set to blue.
There was a bug there; when the auto-generated buttons were used to switch, I assigned the plain URL to style.backroundImage. While it has to be wrapped in 'url(...)'.
I corrected that now, and tried to test it. But I cannot even get a board background to work without any switch buttons. The Diagram in the Comment I am now replying to should use a board background. But instead the board shows up all greyish, like the Comments background color. Even though I set the background color of the <div> that contains the Diagram definition (which will get to contain the container <div> of the board as one of its daughters) to green, the green doesn't shine through.
(I get some sick behavior there too; sometimes the area of the Diagram is all green, as I expect, but then, after a few second, usually at the same time the ads appear, most of the green diappears, and only a tiny bit between the buttons is left.)
It seems that something is not transparent, and that also seems to cover the background image of the board. Any background color I specify for the container <div> also doesn't become visible. So I suppose it is the grid-item <div> elements (i.e. the board squares) that fail to become transparent even when Display assigns an empty string to their style.backgroundColor attribute. When the squares are <td> elements in a table I did not have that problem.
Although the test Diagram there has buttons, the problem already occurs before any of the buttons is pressed, on first parsing of the Diagram. The set lines that define the buttons thus cannot be the problem, these just cause some lines in the definition to be skipped on parsing. And indeed I verified that the behavior remains the same when I delete all these lines.
[Edit] The background (color or image) of the container <div> does not seem to be covered by the background of its daughter items. I can force the latter to a semi-transparent color by using 8-digit color codes for their background, like #FF000080. That gives a pinkish board, showing that the color is indeed used, and that something nearly white shines through. Even though the background color of the container is set to blue.