GDM3 Theme.

Briefly describe your issue below:
How do I change the GDM3 theme on the login screen?
I am using Parrot GNU/Linux 4.4, 64-bit, Security Edition.
I used a DVD, I had downloaded and burned an ISO.
I am only using Parrot Security Linux on my Laptop.

What version of Parrot are you running? (include version, edition, and architecture)

What method did you use to install Parrot? (Debian Standard / Debian GTK / parrot-experimental)

Configured to multiboot with other systems? (yes / no)

If there are any similar issues or solutions, link to them below:

If there are any error messages or relevant logs, post them below:

have you tried the apperance or MATE tweak menus up in the settings bar? if its not up there you can search synaptic for that theme