Ok, I've been trying to set CSS rules that would affect the entire PDF document (as produced by Calibre's Output Filter leveraging the logic of paged.coffee), but no luck.
I'm not giving up, but meanwhile, if you have any idea how one could instruct the webkit-based renderer to apply CSS rules to a PDF page as a whole/unit, that would be great. Especially, something that would target the whole page. It's kind of disappointing setting a simple background for the PDF document has to be so damn hard a task