https://wiki.archlinux.org/index.php/GRUB#Theme
http://wiki.rosalab.ru/en/index.php/Grub2_theme_tutorial
http://wiki.rosalab.ru/en/index.php/Grub2_theme_/_reference

http://www.thelinuxguy.nl/how-tos/how-to-change-the-grub2-theme-on-archlinux/
https://github.com/Generator/Grub2-themes#faq
https://github.com/Generator/Grub2-themes

https://github.com/Jacksaur/Gorgeous-GRUB

https://github.com/EndeavourOS-Community-Editions/grub2-theme-endeavouros-classic

/boot/grub/themes/
/etc/default/grub
GRUB_THEME=/boot/grub/themes/descent/theme.txt
GRUB_GFXMODE=1280x800

collections
https://github.com/jacksaur/Gorgeous-GRUB

BigSur
https://www.pling.com/p/1443844/

Grub-theme-vimix
https://www.pling.com/p/1009236
    https://github.com/vinceliuice/grub2-themes

2022
https://ostechnix.com/change-grub-theme-in-linux/