What is CSS Minifier Tool?
Minifying CSS takes the beautified, well formed CSS code that you have written and removes whitespace, eliminates new lines, strips comments, combines files, and optimizes/shortens a few common programming patterns. These elements are not required for CSS to be used successfully. It also makes the CSS more difficult to read.
The best practice of many developers is to maintain a 'beautified' version, and when rolling out their project will run the styles through a minification program. They will also combine their many style files into one file.