I tried to install SLAVE GTK3 Theme and this is the error msg i am getting. I used the command sudo apt-get install slave-gtk3 for the installation Please someone help in this topic
It doesn't appear to be a standard package. It certainly isn't in any of the standard repositories.
There is one PPA that I can find that provides it: https://launchpad.net/~upubuntu-com/+archive/gtk3
Obviously the standard stuff about PPAs applies. Your computer is only as secure as the software you run on it. PPAs are untrusted sources. Anyway, the choice is yours.