I have select2 customized via css with its general classes and ids.
Now, I\'m trying to customize a specific class that will be provided to select2 and then apply in css
You can use dropdownCssClass for adding class to the select2-drop. I read whole plugin to understand what is going on. Finally, I found that option.
 $(".jSelectbox").select2({
     containerCssClass: "error",
     dropdownCssClass: "test"
 });
$(".jSelectbox").select2({
  containerCssClass: "error",
  dropdownCssClass: "test"
});
Jsfiddle