site/backend/app/templates/_postnav.html

  <div>
  {% if prev_url %}
  <a class="button" href="{{ prev_url }}">Newer</a>
  {% else %}
  <a class="button" aria-disabled=true>Newer</a>
  {% endif %}

  {% if next_url %}
  <a class="button" href="{{ next_url }}">Older</a>
  {% else %}
  <a class="button" aria-disabled=true>Older</a>
  {% endif %}
  </div>