if you specify master=0, then the master templates are not used, which are normally responsible for the output of the HTML head (and other things). So, by deactivating the master, the page has to return a FULL HTML document. The problem is not that the css file is not parsed/found or whatever, but that the header information is omitted. To get a better understanding, look for header_stuff in xowiki-www-procs.tcl.
there is no easy way to get a "full-screen mode" in the general case. One has either to modify the master templates of openacs (e.g. conditionally switching the master templates) or one has to modify the method view to return optionally a full HTML document, containing the header stuff and the page content.