use flex

src/server/views/modal/rename.html

@@ -20,7 +20,7 @@
                 <span class="input-group-text">{{ baseUrl }}</span>
               </div>
               {% if isSearchServiceConfigured() %}
-              <div id="rename-page-name-input" class="page-name-input"></div>
+              <div id="rename-page-name-input" class="page-name-input flex-fill"></div>
               {% else %}
               <input type="text" class="form-control" name="new_path" id="newPageName" value="{{ page.path }}">
               {% endif %}