Backend\Core\Engine\Header::parseCSS PHP Method

    public function parseCSS()
    {
        // init var
        $cssFiles = array();
        $existingCSSFiles = $this->getCSSFiles();
        // if there aren't any JS-files added we don't need to do something
        if (!empty($existingCSSFiles)) {
            foreach ($existingCSSFiles as $file) {
                // add lastmodified time
                if ($file['add_timestamp'] !== false) {
                    $file['file'] .= mb_strpos($file['file'], '?') !== false ? '&m=' . LAST_MODIFIED_TIME : '?m=' . LAST_MODIFIED_TIME;
                }
                // add
                $cssFiles[] = $file;
            }
        }
        // css-files
        $this->tpl->assign('cssFiles', $cssFiles);
    }