Copy/paste the original grub.cfg to have a backup. You will need it later.
Start grub-customizer and choose your theme.
Only the standard theme “starfield” will show up when you start it for the first time.
Choose the theme, save and reboot.
But first we use meld to compare the two files and learn from it.
Dimensions of grub will be
small on virtualbox
This is the vimix theme from gnome-look.org. Found it later on the AUR as grub2-theme-vimix-git.
This is the Arch silence theme from gnome-look.org.
Arch Silence theme is actually in the AUR and lots more are in there. You try them out.
I do not see a setting to set everything back the way it was before grub-customizer. We had made a backup so we can set it now back. Comparing with meld again.
Take a wallpaper as background
I continued to have some fun with a wallpaper I wanted to put as background in the grub.
THINGS CAN GO WRONG
I choose the wrong font here and was able to log back in.