I\'m using Zend Framework and DOMPDF library. When I test it with inline css everything works perfectly. But when I tried to move css code to the external file rules are not
This has in fact nothing to do with Zend Framework, but you need to supply DomPDF the right path to load the "external" files from.
$dompdf = new DOMPDF();
$dompdf->setBasePath(realpath(APPLICATION_PATH . '/path/to/css/'));
$dompdf->loadHtml($html);
$dompdf->render();
See also the manual of DomPDF for this feature.