Can you have a php include inside a php include? Also, can you have a css file in a php include, and just link to the php include on your page and not the stylesheet individually on each page?
You can include an include within an include ( if that makes sense) It however is best to use CSS includes as you would in the head as the borwser will cache the file localy for the users and will increase the speed of you site.
I suppose that using an include for the CSS page would be similar (to browsers) to having your CSS be inline? Not sure what the point to doing it could be, but I don't see why you couldn't make it work.
Sure, it's be the same as having it inline but the point made by ServerUnion was that calling for it in the head would allow your browser to cache it and save bandwidth and page loading time.
That's why I said I didn't see what the point in using a php include would be, but I suppose the original poster has a reason for this.