@ikerr The Recalbox Team is only responsible for the default theme, which comes with Recalbox.
User-created themes are centered in the section:
https://forum.recalbox.com/category/14/themes-interface
I don't know if there is a theme that meets the requirements you want, but one of the most popular themes is:
https://forum.recalbox.com/topic/16064/recalbox-8-theme-next-pixel
It has a lot of information, it has documentation, and the creator usually answers most users' questions, check it out.