fix style bug

src/styles/core/extend.css

@@ -1,4 +1,8 @@
 /* bootstrap */
+.btn-group + .btn {
+    margin-left: 4px;
+}
+
 .progress-bar {
     -webkit-transition: initial !important;
     -moz-transition: initial !important;

src/views/task-detail.html

@@ -210,8 +210,7 @@
                                         <li><a href="javascript:void(0);" ng-click="selectFiles('none')" translate>Select None</a></li>
                                         <li><a href="javascript:void(0);" ng-click="selectFiles('reverse')" translate>Select Invert</a></li>
                                     </ul>
-                                </div>
-                                <button class="btn btn-xs btn-default" ng-click="chooseSpecifiedFiles('video')">
+                                </div><button class="btn btn-xs btn-default" ng-click="chooseSpecifiedFiles('video')">
                                     <i class="fa fa-file-video-o"></i>
                                     <span translate>Videos</span>
                                 </button>