The icons used are Gnome Desktio icons

https://commons.wikimedia.org/wiki/GNOME_Desktop_icons
gnome-icon-theme 2.20.0

GNOME Desktop icons contains the default icon theme used by the GNOME desktop. The icons are used in the panel menu, and in nautilus and other applications, to represent the different applications, files, directories, and devices. Below are all unique icons from gnome-icon-theme 2.20.0. All icons are licensed under GNU General Public License version 2.



