[GrannyGrump]

I've used Flight Crew and EpubCheck many times, but this was my first time to use the W3C service.

Flight Crew and epubCheck report "No errors found"
but W3C gives me this message:

Error:
URI : TextArea 1
Value Error : margin Parse Error [empty string]
Warning:
URI : TextArea 1
No declarations in the rule

The CSS entry is:
@page {margin: 5pt;}

What have I done wrong, and how do I fix it?

Thanks for any advice.