Install cleancss by entering the following commands in the terminal:
sudo apt update sudo apt install cleancss
Tool for minifying CSS files
Clean-css is a Node.js module for minifying CSS files. It does the same job as YUI Compressor's CSS minifier, but much faster thanks to many speed optimizations and Node.js' V8 engine. . The cleancss tool is a reference implementation for the Clean-css Node.js module.