Hi C-Beats,
Thank you for your help.
I'm using Launchbox version 12.16 and, despite what is shown in the photo I posted earlier, I have the premium license.
I believe I made a mistake in thinking the themes were not being applied.
What happened, I believe, is that the images that Launchbox brings as a preview of each theme have images of random games in the background, in a blurred way.
It happened that I still couldn't enable this type of visual effect (make the game image appear in the background, when I select this game's icon).
Anyway, thanks for the help!