My comments more appropriate for tech support
or Becoming Conversant
but there should be a couple of workarounds for users without access to a static server. For example, those who are trying free hosting through Macrobyte. I haven't tested either of these.
First workaround: write your stylesheet as a text file and upload it as a message enclosure, then link to that message enclosure.
Second workaround: write your stylesheet as a discussion group message. Bind it to an URL. Go into the admin system, locate the bound URL, and click on the "Basic" tab. Change the MIME type on the bound message to "text/css" and click "submit". Link to your bound URL.
I think Clark's comments on the needs for workaround are on the money. That said, it's an amazing thing about Conversant's flexibility that an end user like me who can barely program macros right can hack the default install as much as I am able to hack it. Brian Carnell has referred to Conversant both as Legos and as a Transformer. The home page for Voices of Unreason is built out of a bunch of queries using Conversant's amazing search engine to dynamically serve it.
As developers I hope y'all discover just as much flexibility under the hood. I've never regretted moving to Conversant, in part because I know if I need it to do something for me it can be made to do that thing.