To use this theme, edit /etc/sysconfig/grub to include:
GRUB_THEME="/boot/grub2/themes/breeze/theme.txt"
and comment-out line:
GRUB_TERMINAL_OUTPUT="console"
Then, run
grub2-mkconfig -o /boot/efi/EFI/fedora/grub.cfg
if using EFI, otherwise,
grub2-mkconfig -o /boot/grub2/grub.cfg