W3C stylesheets

Hi,

First of all I would like to say I really love your website.

I've got a question I couldn't solve searching on the internet nor in  
CSS IRC (freenode). I would like to use a "base.css" stylesheet for my  
web pages, and then, depending on the browser's width, apply another  
stylesheet "mobile.css" or "advanced.css". Can I do that? How? I'm  
getting crazy... ;-)

I took a look at W3C's header but didn't get how it works and why it  
uses two links for "min.css" (one at the beginning and the other at  
the end), although I've tried it and see that it works (adding  
"advance.css" to the already in use for all screens "min.css"). I  
don't even know if I understood this well...

Thanks in advance for your help and sorry for my English.

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