This question may be subjective but I am having problems selecting GTK3 Themes using My Unity.
Some GTK3 Theme installation instructions ask you place the extracted theme folder in ~/.Themes (hidden in your home folder) and here is where the problem starts (for My Unity). I have to use Advanced Settings (Gnome Tweak tool) to select themes from the home folder to get the theme working correctly.
When I review the selected Theme in My Unity it places a big red X beside the selected theme name. Themes installed in ~/.Themes DO NOT work correctly when selected in My Unity
I resolved this by ignoring GTK3 installation instructions and copying the same theme folders to usr/share/themes using Sudo Nautilus. These themes work perfectly now when selected in My Unity. Does anyone know why this behavior happens in My Unity (when themes are placed in ~/.Themes, and can it be fixed. This is not machine specific as it happens on my daughters laptop as well.