[www-validator-css] <none>

I am just starting to use CSS1, and have attempted to validate
http://www.tassie.net.au/abell1/oboe.css which is an external file called by
oboe.htm. 

I get the error message Unknown mime type : text/plain

but do not know why.  Should I put something actually in oboe.css to show
that it is text/ccs?

Regards, Alex

PS My main e-mail address is abell1@tassie.net.au