Set top level comment to replace entire section after successful post

tildes/tildes/templates/topic.jinja2

@@ -213,12 +213,13 @@
 {% endif %}
 
 {% if request.has_permission('comment', topic) %}
-  <section>
+  <section class="post-top-level-comment">
     <h2>Post a comment</h2>
     <form
       method="post"
       data-ic-post-to="{{ request.route_url('ic_topic_comments', topic_id36=topic.topic_id36) }}"
       data-ic-replace-target="true"
+      data-ic-target=".post-top-level-comment"
       autocomplete="off"
       data-js-prevent-double-submit
       data-js-confirm-leave-page-unsaved