No stylesheet or pop-up for "Selected Events" page/option

I have created an event and all is in order besides the "Selected Events" page/option which is missing a stylesheet or the "Selected Events" is not showing in a popup window (see screenshot below)

Link to event page: psanamibia.org/en/events/the-authentic-c...authentic-stage-info
Link to "Selected Events" page: psanamibia.org/en/events/the-authentic-c...k=cart.add_cart&id=3

Any help with either assigning this page to a standard Joomla! template page or (more ideally) as a pop-up window, would be greatly appreciated, thanks.