From here.
The following instructions are tested on my Ubuntu 16.04 Xenial environment.
- Download macOS Sierra GTK Theme from Github. In my case, I download “OS.X.El.Capitan.v0.9.tar.gz“. Extract the tar file and copy the extracted directory into your “ - /.themes” directory. If “/.themes” doesn’t exist, create it first.
- Download La Capitaine Icon Set on Github. In my case, I download “la-capitaine-icon-theme-0.4.0.tar.gz“. Extract the tar file and copy the extracted directory into your “ - /.icons” directory. If “/.icons” doesn’t exist, create it first.
- Clone the “capitaine-cursors” project from here. Copy the cursors by running the “cp -pr bin/xcursor ~/.icons/capitaine-cursors” command. 
- Open “Unity Tweak Tool”, change theme in “Appearance -> Theme”, icon in “Appearance -> Icons”, and cursor in “Appearance -> Cursors”. 
- From here you can find some more themes, such as this “papirus-icon-theme“ one. Install it by running the following commands: 
| 1 | sudo add-apt-repository ppa:papirus/papirus | 
Done.