gnome-extra-icons software package provides Optional GNOME icons, you can install in your Ubuntu 16.04 LTS (Xenial Xerus) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install gnome-extra-icons
gnome-extra-icons is installed in your system.
Make ensure the gnome-extra-icons package were installed using the commands given below,
$ sudo dpkg-query -l | grep gnome-extra-icons *
You will get with gnome-extra-icons package name, version, architecture and description in a table
| Distro | Ubuntu 16 04 lts xenial xerus |
| Section | GNOME |
| Package | gnome-extra-icons |
| Version | 1.1-2 |
| Description | Optional GNOME icons |
| Sub Section | GNOME |