Added support for the shadowdom

src/js/select2/dropdown/attachBody.js

@@ -195,7 +195,7 @@ define([
       left: 0
     };
 
-    if ($.contains(document.body, $offsetParent[0])) {
+    if ($.contains(document.body, $offsetParent[0]) || $offsetParent[0].isConnected) {
       parentOffset = $offsetParent.offset();
     }