I haven't really made themes in a long time. But all of my older ones are still on my Github. I wasn't the best theme programmer back then, but they seemed to work okay.
https://github.com/dmmarti?tab=repositoriesI use Attract Mode in a nested menu (so I have Main Menu > Sub Menu > Systems Menu).
Main Menu and Sub Menu would use the same theme.
Main Menu => Computers, Consoles, Arcades, etc
Sub Menu => (would list all systems of the same type, ie: Atari 2600, NES, Megadrive, etc for Consoles)
System Menu => for viewing individual system's games
My naming convention on my GitHub let's you know which one that theme is for.
I have AM themes, ES themes, as well as system media PNGs on my Github.
For the AM themes, here's the naming convention (and you'll see _menu or _systems in it's name if needed, otherwise, it's a global use theme).
am-theme-XXXXXX
I also made RetroPie ES themes that are included in the RetroPie theme downloader script.
Then there's a bunch of repos for system media files (wheels, flyers, backgrounds, etc.) that could be used in all sorts of ways.