Merge pull request #2472 from Leopoldthecoder/messagebox-class

MessageBox: add default customClass, fixed #2438

packages/message-box/src/main.js

@@ -21,6 +21,7 @@ const defaults = {
   cancelButtonText: '',
   confirmButtonClass: '',
   cancelButtonClass: '',
+  customClass: '',
   beforeClose: null
 };