Gnome Cupertino theme originally created by Rafa Cobreros and recently it was ported to Gtk 3.10 by bluedxca93 for 14.04. Few days back I tested this theme that time it was in alpha phase which means a lot of bugs but a new update brought a lot of fixes and now it works properly with Ubuntu 14.04 Trusty. It also has Gnome Shell theme which is compatible with Shell 3.12/3.10/3.8 but not really appealing version, I also tested this theme in Xfce check out screenshots below.
You can use Unity Tweak ToolGnome-tweak-tool or Ubuntu-Tweak to change themes.
gnome cupertino

gnome cupertino

gnome cupertino

gnome cupertino

>> Gnome Cupertino theme is available for Ubuntu 14.04 Trusty and Ubuntu 12.04 Precise
To install Gnome Cupertino theme in Ubuntu/Linux Mint open Terminal (Press Ctrl+Alt+T) and copy the following commands in the terminal:
That's it
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