🆕 Adjustable fill colour for iframe containing the BASIC console window

 When whatever container (browser window, <div>) is resized, that will cause the iframe to get resized to whatever new 100% of the height and 100% of the width of the container.

And when the iframe resizes, the BASIC console window will also get resized, but the console will maintain scaled proportions for width and height based on whatever screen settings for the console window.

Whatever extra space exists between the iframe and the console window, that space normally gets filled with a gray colour (#aaaaaa).

Now, you can customise that colour via a BASIC program's File Properties.

The primary purpose for this feature: embedding BASIC Anywhere Machine programs in web pages (and TiddlyWiki) in way that fits the target colour-wise.