/* Minify CSS */
function minifyCSS($string){
 
    /* Strips Comments */
    $string = preg_replace('!/\*.*?\*/!s','', $string);
    $string = preg_replace('/\n\s*\n/',"\n", $string);
 
    /* Minifies */
    $string = preg_replace('/[\n\r \t]/',' ', $string);
    $string = preg_replace('/ +/',' ', $string);
    $string = preg_replace('/ ?([,:;{}]) ?/','$1',$string);
    return $string;
}

http://kitmacallister.com/2011/minify-css-with-php/

As simple as it can be. An PHP minifier. All the credits go to his author, Kit MacAllister

Minify CSS With PHP

css, php

PHP