Prevent drag item hover styles on touch devices.

It can be confusing when the outline is drawn around the item that you
just tapped, even though the item is not draggable at that point.

drag_and_drop_v2/public/css/drag_and_drop.css

@@ -726,3 +726,12 @@
     background-color: #ffffff;
     color: #000000;
 }
+
+
+/* Prevent mobile browsers from emulating hover effects on item tap, which can be confusing. */
+@media (hover: none) {
+    .xblock--drag-and-drop .drag-container .option[draggable='true']:hover {
+        outline: none;
+        box-shadow: none;
+    }
+}