I am creating a wiki page with MediaWiki and would like to use the OOUI Library to create widgets like this drop down menu. However, I am not sure how to use the code. I created a a widget page and copied the code for the drop down menu in this widget. When I called that widget like this:

{{#widget: DropdownMenu}}

the wiki page just copied the drop down menu code.

Here is what the page looks like when I call the widget:

I have read through the documentation and can not find any information regarding what files to place the widget code. Any help would be really appreciated.