Add CSS to DomPDF

I've got this code to export some data into a pdf. And I would like to add css from an external css file (which is not mentionned in the html used)

/*********************************** Export PDF ****************************************************/
if($request->query->get('exportPDF')!= null){
    // Configure Dompdf according to your needs
    $pdfOptions = new Options();
    $pdfOptions->set('defaultFont', 'Arial');
    // Instantiate Dompdf with our options
    $dompdf = new Dompdf($pdfOptions);
    // Retrieve the HTML generated in our twig file
    $html = $this->renderView('dashboard/user_table.html.twig', [
        'users' => $users
    // Load HTML to Dompdf
    $dompdf->loadHtml($html);
    // (Optional) Setup the paper size and orientation 'portrait' or 'portrait'
    $dompdf->setPaper('A3', 'landscape');
    // Render the HTML as PDF
    $dompdf->render();