Adding to what @Ravi already answered:
From primefaces 3.0 on you can customize the order of the resources. However when I tried that it was not working at first.
It turned out that I could not use the JSF component to include css like this:
Instead I had to use:
Only then the ordering started to work.
EDIT: My answer is superfluous if you put the facet into the body (instead of head). Just like Ravi wrote in his answer. (I must have missed that somehow.)
It also not advisable to do this because then the resources are not processed by the FacesServlet and problems with paths inside of css can come up. Compare this answer from BalusC.
