Most of the themes created for EmulationStation aren't formatted for the specific screen size of the Retroflag GPi case. This one is!
It's created in the style of the original Dot Matrix Game Boy.
Save the theme files to either:
$HOME/.emulationstation/themes//etc/emulationstation/themes/
A video splash screen is provided in the /splash folder.
Save the file in the splashscreens samba share folder, and then set it in the settings GUI.
Gamegirl Classic from https://www.fontspace.com/gamegirl-classic-font-f3331
Coin05 from https://taira-komori.jpn.org/