This page covers the changes I made to SDDM — the login screen used on my setup.
There are many themes for SDDM and you can find them by searching in google or github. I will be installing sddm-astronaut-theme
To install you just have to run
sh -c "$(curl -fsSL https://raw.githubusercontent.com/keyitdev/sddm-astronaut-theme/master/setup.sh)"
It should take care of rest of the work.