You are using a location that is already part of the current application. Service Studio doesn't support that as far as I know and you will need to add that css content to the regular OutSystems css file (by using the css button in the menu bar).
edit: Now that I think about it more I don't think this will ever work. OutSystems doesn't render a webpage, it presents a wysiwyg look of the page you develop based on the data already available. Retrieving external data isn't part of that so I don't think this will ever work, even on 11.