flask-debugtoolbar/flask_debugtoolbar/templates/panels/headers.html

<table>
  <thead>
    <tr>
      <th>Key</th>
      <th>Value</th>
    </tr>
  </thead>
  <tbody>
    {% for key, value in headers|dictsort %}
      <tr class="{{ loop.cycle('flDebugOdd', 'flDebugEven') }}">
        <td>{{ key|escape }}</td>
        <td>{{ value|escape }}</td>
      </tr>
    {% endfor %}
  </tbody>
</table>