Tested on Debian 13 (Trixie)
How to install.
First, you download this theme from pling.com
Download
Second, extract the zip files to your desired location (in my case ~/Downloads)
Third, go to terminal type
cd ~/path-to/grub2-theme-vimix
Change path-to to your desired location.
Installing
Type
chmod +x install.sh
Then
sudo install.sh
And done!

Sources
vinceliuice