Fixed preview overflow issue.

apps/devhub/templates/devhub/addons/submit/media.html

@@ -66,11 +66,12 @@
         <div id="file-list">
           {% for form in preview_form.forms %}
           <div class="preview">
-            <div class="preview-thumb">
-              {% if form.instance.id %}
-                <img src="{{ form.instance.thumbnail_url }}">
-              {% endif %}
-            </div>
+            {% if form.instance.id %}
+              <div class="preview-thumb" style="background-image:url({{ form.instance.thumbnail_url }})">
+              </div>
+            {% else %}
+              <div class="preview-thumb"></div>
+            {% endif %}
             {{ form.id|safe }}
             <span class="js-hidden delete">{{ form.DELETE|safe }}{{ form.DELETE.label_tag()|safe }}</span>
             <div class="edit-previews-text">

apps/devhub/templates/devhub/includes/addon_edit_media.html

@@ -86,11 +86,12 @@
                     {% for form in preview_form.forms %}
                       <div class="preview">
                         <span class="handle">&nbsp;</span>
-                        <div class="preview-thumb">
-                          {% if form.instance.id %}
-                            <img src="{{ form.instance.thumbnail_url }}">
-                          {% endif %}
-                        </div>
+                        {% if form.instance.id %}
+                          <div class="preview-thumb" style="background-image:url({{ form.instance.thumbnail_url }})">
+                          </div>
+                        {% else %}
+                          <div class="preview-thumb"></div>
+                        {% endif %}
                         {{ form.id|safe }}
                         <span class="js-hidden delete">{{ form.DELETE|safe }}{{ form.DELETE.label_tag()|safe }}</span>
                         <div class="edit-previews-text">
@@ -118,9 +119,7 @@
                 {% endif %}
               {% else %}
                 {% for preview in addon.previews.all() %}
-                  <div class="preview-thumb">
-                    <img src="{{ preview.thumbnail_url }}">
-                  </div>
+                <div class="preview-thumb" style="background-image:url({{ preview.thumbnail_url }})"></div>
                 {% endfor %}
               {% endif %}
             </td>