Minify-CSS.php

<?php
function minify_css($css_code)
{
    // Remove comments
    $css_code = preg_replace('!/\*[^*]*\*+([^/][^*]*\*+)*/!', '', $css_code);

    // Remove space after colons
    $css_code = str_replace(': ', ':', $css_code);

    // Remove whitespace
    $css_code = str_replace(array("\r\n", "\r", "\n", "\t", '  ', '    ', '    '), '', $css_code);

    // Remove Empty Selectors without any properties
    $css_code = preg_replace('/(?:[^\r\n,{}]+)(?:,(?=[^}]*{)|\s*{[\s]*})/', '', $css_code);

    return $css_code;
}