Install famfamfam-silk by entering the following commands in the terminal:
sudo apt update sudo apt install famfamfam-silk
Description:
smooth, free icon set, with over 700 16x16 pixel icons
"Silk" is a smooth, free icon set, containing over 700 16-by-16 pixel icons in strokably-soft PNG format. Containing a large variety of icons, you're sure to find something that tickles your fancy.
Homepage: http://www.famfamfam.com/lab/icons/silk/
Version: 1.3-1
Section: universe/misc