Lakka Theme and wallpaper creation for Raspberry Pi 4B

I want to create a custom background for my Raspberry Pi 4B running Lakka OS. Since the RPi4 has better hardware than the previous versions and can handle more what is the best resolution for making a background for it? As for Themes can the icons be bigger than what they were before? Please some specifications would be appreciated. Im starting with a background but I would like to expand into a theme for it.

Would color fonts work? https://www.fontspace.com/category/color