$ sudo apt-get update
$ sudo apt-get install gnome-themes-standard 

gnome-themes-standard is installed in your system.

Make ensure the gnome-themes-standard package were installed using the commands given below,

$ sudo dpkg-query -l | grep gnome-themes-standard *

You will get with gnome-themes-standard package name, version, architecture and description in a table

gnome-themes-standard package basic information: