Merge branch 'develop' into minor-ui-improvement

css/less/workspace.less

@@ -28,6 +28,9 @@
 
     .remove-slot-option {
       position: absolute;
+      top: 0;
+      left: 0;
+      z-index: 1;
       margin: 10px;
       color: @gray;
       cursor: pointer;