Exemple taken from CCS3 spec:
http://www.w3.org/TR/css3-page/#page-box-page-rule

@page {
  size: A4 landscape;
}

Output of CSS validator:

Errors when validating /tmp/print.css
{output=text, lang=en, warning=2, medium=all, profile=css3}
W3C CSS Validator results for file:/tmp/print.css
            
Sorry! We found the following errors (1)

URI : file:/tmp/print.css

Line : 2 
       Parse Error
       [empty string]

Warnings (1)

URI : file:/tmp/print.css

Line : 3 -  No declarations in the rule

Valid CSS information
    
@page
{
                                                    
}