Install cssmin by entering the following commands in the terminal:
sudo apt update sudo apt install cssmin
YUI CSS compression algorithm (command line tools)
cssmin is a Python port of the YUI Cascading Style Sheet (CSS) compressor. The compressor can be used to reduce the size of CSS documents for deployment. . This package contains the command line tools for cssmin. See the python-cssmin and python3-cssmin packages for the Python modules.