You additionally need an “Xfwm4” theme if you are gonna use Xfce, or your window controls will look different than your GTK theme.
However, the GTK/Qt theme used is not everything, as most desktops tend to develop their own “window managers” and other interface components, which will require you get additional themes for each of these components. You can get GTK and Qt themes from many sources and websites on the Internet to make your system look more stylish according to your taste. There are 2 famous toolkits that are widely used in Linux: GTK and Qt. In the Linux world, desktop environments use something called “user interface toolkits” to develop menus, panels and applications.
