CSS Comp.

gistfile1.php

<?php

define('CSS', '/css/compiled');

define('CSS_PATH', realpath(__DIR__ . '/css'));

define('CSS_COMPILED', realpath(CSS_PATH . '/compiled'));

function css($css)
{
    $name = md5(implode('', $css)) . '.css';

    if ( ! is_file(CSS_COMPILED . '/' . $name)) {
        $out = '';

        foreach ($css as $file) {
            $out .= file_get_contents(CSS_PATH . '/' . $file);
        }

        $out = preg_replace('!/\*[^*]*\*+([^/][^*]*\*+)*/!', '', $out);
        $out = str_replace(': ', ':', $out);
        $out = str_replace(array("\r\n", "\r", "\n", "\t", '  ', '    ', '    '), '', $out);

        file_put_contents(CSS_COMPILED . '/' . $name, $out);
    }

    return CSS . '/' . $name;
}

echo css(['body.css', 'h1.css', 'p.css']);

echo css(['body.css', 'p.css']);