Adwaita Cupertino Flavors is a set of GTK3 and window manager themes that are heavily inspired by Mac OS design.
The set includes many different variations, darker and lighter, with slightly different button size etc. If you want to make your Gnome desktop look like a Mac, then this theme is the right choice for you.
To install and use these themes extract the Adwaita Cupertino Flavors.tar.gz andcopy extracted folders to /.themes. You can then use the Advanced Settings menu and choose it from GTK+ theme tab. If that sound too complicated you should check our comprehensive guide on how to theme Gnome 3.