Install gnome-icon-theme-symbolic by entering the following commands in the terminal:
sudo apt update sudo apt install gnome-icon-theme-symbolic
Description:
GNOME desktop icon theme (symbolic icons)
This package contains a set of icons 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. . These stylised icons are symbolic variations on the standard theme.
Homepage: https://wiki.gnome.org/Design/OS/SymbolicIcons
Version: 3.12.0-2
Section: universe/gnome