WIP: collapse while being dragged

contribs/gmf/less/desktoplayertree.less

@@ -49,17 +49,6 @@ gmf-layertree {
     }
   }
 
-  &.gmf-layertree-dragger {
-    * {
-      cursor: url(../cursors/grabbing.cur), default;
-      cursor: -webkit-grabbing;
-      cursor: grabbing;
-    }
-    ul {
-      display: none;
-    }
-  }
-
   .gmf-layertree-group.gmf-layertree-depth-1 {
     background-color: @main-bg-color;
     padding: @half-app-margin;
@@ -119,3 +108,16 @@ gmf-layertree {
   margin: 0 @micro-app-margin @app-margin @micro-app-margin;
   box-shadow: 0 0 4px 1px @input-border-focus;
 }
+
+/* super specific, to have a higher precedence order than the collapse rule */
+.ui-sortable .gmf-layertree-node.gmf-layertree-dragger {
+  * {
+    cursor: url(../cursors/grabbing.cur), default;
+    cursor: -webkit-grabbing;
+    cursor: grabbing;
+  }
+  /* FIXME: ul doesn't get properly hidden, despite being the active rule */
+  ul.collapse.in {
+    display: none;
+  }
+}