CSS applied by a javascript

http://jigsaw.w3.org/css-validator/validator?uri=http://www.oclc.org/home/
<http://jigsaw.w3.org/css-validator/validator?uri=http://www.oclc.org/home/>

 
We have a problem using the validator.  We use a javascript to detect which
CSS to apply based on browser, due to display differences (relative-sized
fonts in Netscape browsers are much smaller than in IE, for example).
Because of this, it seem that the validator does not recognize that a style
sheet is being applied.  It only finds the single style described in the
head of the document.
 
Is there a "browser" that your validator emulates?  Could be we aren't
"sniffing" it out and applying a CSS?  Or, it could be that the validator
doesn't work with this type of setup?
 
Mickey Hawk
Art Director/E-Media
OCLC Online Computer Library Center, Incorporated
Dublin, OH
mickey_hawk@oclc.org <mailto:mickey_hawk@oclc.org> 
www.oclc.org <http://www.oclc.org/>