If you are a git user, you can install the theme and keep up to date by cloning the repo:
git clone https://github.com/dracula/grub.git
Download using the GitHub .zip download option and unzip them.
- Move the crystal folder to /usr/share/grub/themes/
- Change the theme in /etc/default/grub ( Set GRUB_THEME to '/usr/share/grub/themes/crystal/theme.txt')
- Run
sudo grub-mkconfig -o /boot/grub/grub.cfg