git clone https://github.com/Tihmz/evangelion-grub-theme.git
sudo cp -r evangelion-grub-theme /boot/grub/themes/
Then edit the file /etc/default/grub
and change the following line :
[...]
GRUB_THEME=/boot/grub/themes/evangelion-grub-theme/theme.txt
[...]
Finally, update your grub configuration with sudo update-grub
Simply delete the folder and remove the line :
sudo rm -rf /boot/grub/themes/evangelion-grub-theme
sudo sed -i '/^GRUB_THEME/d' /etc/default/grub
sudo update-grub
Inspired by the following theme : https://github.com/shvchk/fallout-grub-theme