Here's how you can install the GNOME Cupertino theme in Ubuntu 14.04.
1. Open a terminal window.
2. Type in the following commands then hit Enter after each.
sudo add-apt-repository ppa:noobslab/themes
sudo apt-get update
sudo apt-get install gnome-cupertino
According to Noobs Lab:
Gnome Cupertino theme originally created by Rafa Cobreros and recently it was ported to Gtk 3.10 by bluedxca93 for 14.04. You can use Unity Tweak Tool, Gnome-tweak-tool or Ubuntu-Tweak to change themes.More at Noobs Lab
Additional Ubuntu resources