The people who are wanting to use this in Linux Mint Cinnnamon 20. first you must install lightdm-gtk-greeter and its settings by this command sudo apt install lightdm-gtk-greeter...

I think the file you need to edit is /etc/lightdm/lightdm.conf.

extract to /usr/share/themes/. must be root or sudo. There is an app to configure lightDM. https://packages.debian.org/search?keywords=lightdm-gtk-greeter-settings There is a way to configure...

How do I install this?

Wonderful !! Thank you sir !