reNIX is a beautiful GTK3 theme inspired by Android. The theme is compatible with latest Unity and Gnome Shell and comes with a squared metacity theme.
To install, extract the archive to the themes directory i.e. "~/.themes/" or "/usr/share/themes/".
Use Gnome Tweak tool or Ubuntu Tweak to choose the themes.
You can also install a matching theme for Chrome/Chromium from here.