This is more specific to Pagoda Box than CSS in general, but you can do it by setting your httpd_document_root in your Boxfile. Here’s an example:
Your app directory will then become your “web root” and load when you go to your domain. Know however that you can only have one document root in a single web. So with this setting, the test directory won’t be accessible through your browser.
If you needed that to be publicly accessible as well, you’d have to create a second web service and set its httpd_document_root to test.