I installed Ubuntu GNOME 16.04 LTS and I'm having trouble trying to figure out how to apply a GTK theme to GDM. In my searches for an answer I have seen a couple of times that GDM has discontinued theme support, but it seemed as though that was referring to themes specific to GDM, rather than general gtk themes.
I've already attempted a couple of things:
I had read you can customize gdm through Ubuntu tweak, so I followed these instructions: http://ubuntuhandbook.org/index.php/2016/05/install-ubuntu-tweak-in-ubuntu-16-04/ unfortunately I couldn't figure out how to do much of anything with it
I modified "greeter.dconf-defaults" under the GDM directory in /user/share where it specifically mentions gtk themes with nano (screen-cap of the file and its location) though I'm not positive I have the syntax correct
I looked for a graphical way to do it and I found GDM3Setup but it seems it doesn't support Ubuntu 16.04 LTS and the Software app won't install the .deb for Ubuntu 15.04.