These themes I am installing in this screenshot are very high quality GTK 3 themes that are perfect for your Gnome Shell desktop.The Greybird one is the theme that I am using at the moment. It looks very good indeed with a dark GTK theme and window decoration. Installing themes this way is easier than downloading them off the Internet and installing them only to find that they do not style GTK 3. There are countless GTK 2.0 themes that are very nice indeed, but not as many GTK 3.0 themes and this shows that the installation of GTK themes need not be difficult at all, that is what Linux is about.