Download the tar archive from the Files(1) tab above and extract the contents to the theme directory of SDDM (change the path for the downloaded file if necessary):

$ sudo mkdir ‑p
/usr/share/sddm/themes

$ sudo tar ‑xzvf
~/Downloads/transparent-sddm-0.1.tar.gz
‑C
/usr/share/sddm/themes

This will extract all the files to a folder called "transparent-sddm-0.1" inside of the themes directory of SDDM.

After that you will have to point SDDM to the new theme by editing its config file, preferrably at
/etc/sddm.conf
In the
[Theme]
section simply add the themes name to this line:
Current=transparent

To use the virtual keyboard simply add in the
[General]
section
InputMethod=qtvirtualkeyboard