Oops, sorry, I hit reply too soon.
Styling of stuff in a side bar uses the
\cat ... \cat* USFM marker to pick a category (see also Categories.md) and a stylesheet-like file to define what that category of sidebar looks like, see
mycats.sty in the above directory.
If you load it with this command, below, rather than
\stylesheet then it takes care of some house-keeping for you.
Alternatively, make sure your stylesheet ends with
I don’t think the GUI has much support for editing category sheets by hand, but notice that you can - within a category - redefine how a (any!) marker behaves - thus the
\p markers in the pink-background boxes are centred, but normal
\p markers are not.
Background images and the
\FgImage ‘category marker’ mentioned in the
sidebars.md document you found are not yet implemented, but borders and background colour are. So far turning on
\Breakable has been an unmitigated disaster… I think I understand why the disaster happens, just not how to resolve it.