A stellar theme for the Anbernic RG35XX Contains a boot logo and a full theme. Might need some tweaks on your end for localisation and a decent list of games (depending on your game art). See instructions below.
Preview of the theme:
Boot logo preview:
Simply drag the skin, lang and font into the CFW folder on your SD card. It'll ask you to replace a bunch of files, hit yes. If you want the dark mode, you will need the 'skin --dark' folder, you can remove the 'skin' folder from your download and rename the 'skin --dark' to just 'skin'.
Replace the boot logo file in the misc partition
Drag the retroarch folder into your CFW folder, it should merge the needed files too. After booting your RG35XX, head into RetroArch/SETTINGS, then pick settings in the list. Select 'User interface', 'Appearance', set 'Menu color theme' to 'Custom' and then 'Custom Menu Theme Preset' to 'Orbital'. That should do it. There's also a dark version of this, just copy over the --dark version instead of the regular one, but don't forget to remove --dark from the folder name.
Replace the ramdisk.img file in the misc partition and drag the entire battery folder in there too.
Currently, the theme is adjusted to have boxart next to your titles. If you downloaded the Tiny Best Set and are looking for a cropped view of box arts, this might help: click Otherwise, you can always align the titles to the center by changing the settings.json in the skin folder. Text-margin should be lowered to 30 and text-alignment changed to center.