A minimalistic GRUB theme inspired by Breeze.
Copy the "breeze" directory to a location GRUB can access it. The standard path is /usr/share/grub/themes/, but if your installing this theme in an encrypted system, you might prefer to copy this package content to /boot and set your GRUB configuration file accordingly.
Edit /etc/default/grub, making sure this line (or a variant of it) exists:
GRUB_THEME="/usr/share/grub/themes/breeze/theme.txt"
And then run:
sudo grub-mkconfig -o /boot/grub/grub.cfg