function _addCSS($order, $resource, $is_file, $minify)
{
$order = intval($order);
$resources = array();
if (array_key_exists($order, $this->css_resources)) {
$resources = $this->css_resources[$order];
}
$css = new CSS($resource, $is_file);
$css->setMinified($minify);
$resources[] = $css;
$this->css_resources[$order] = $resources;
}