rssguard/resources/skins/dark/html_single_message.html

<div class="panel panel-default">
  <div class="panel-heading">
    <h4 class="card-title">%1 <a class="btn btn-primary btn-sm" href="%3">URL</a> %6</h4>
  </div>
  
  <div class="panel-body" dir="auto">
    <div style="padding: 2px; margin: 0px;">
      %7
    </div>
    %4
  </div>

  <div class="panel-footer" style="text-align: center;">
    %2, %5
  </div>
</div>