title: wkhtmltopdf repeatitive background image on all pages
body: <p>I am struggling to make a repetitive background for a generated PDF.</p>
  
  <p>I have a certificate that is automatically generated and certificate design has a frame that should repeat on all the pages...</p>
  
  <p>I tried </p>
  
  <pre><code>.main_container{
     background: url({{ resourceDir ~ 'img/certificate_margin.jpg' }}) 0 0;
     padding-top:15px;
     z-index: 99;
     background-size: cover;
     width:658px;
     height:975px;
  }
  </code></pre>
  
  <p>but after the first page is displayed I only get the content and a white page.
  Did anyone managed to solve this issue some how? Or is it even possible to do it?</p>
  
  <p>my config file:</p>
  
  <pre><code>knp_snappy:
      pdf:
          enabled:    true
          binary:     "%wkhtmltopdf_binary_path%"
          options:
              page-size: A4
              dpi: 150
              image-dpi: 150
              encoding: utf-8
  </code></pre>
  
  <p>and generation code:</p>
  
  <pre><code>$unsignedPdfContent = $this-&gt;snappy-&gt;getOutputFromHtml(
      $this-&gt;templating-&gt;render(
          $this-&gt;getTemplate(), [
              'certificate' =&gt; $this-&gt;certificate,
              'resourceDir' =&gt; __DIR__.'/../Resources/public/'
          ]
      )
  );
  </code></pre>