Install grub-theme-breeze by entering the following commands in the terminal:
sudo apt update sudo apt install grub-theme-breeze
Description:
Breeze theme for Grub 2
Breeze theme for Grub system boot loader to fit in with KDE Plasma's themeing.
Homepage: https://projects.kde.org/projects/kde/workspace/breeze-grub
Version: 5.12.4-0ubuntu1
Section: universe/kde