@mitu this was it. After digging in I did find the same problem and was able to just swap the <theme> tag and get it working

@BuZz Ok no problem, i understand. Thanks.

you edit the config.txt file with some of these settings:

https://www.raspberrypi.org/documentation/configuration/config-txt/video.md

Editing the es_systems.cfgjust for one theme seems like a stupid idea IMO, because it will break probably all other themes that require the snes folder.
I just looked at the retrorama github and would suggest to rename the snes folder to snesntsc and the snespal folder to snes. That should work.