visual studio 2012 - Warning/Error in my css file: css3 document is not a known @ directive -

i getting message in css file while trying use media queries. here code sample:

@document url('http://www.inserthtml.com/')  {         /* css goes here */   }

visual studio 2012 underlines in red , gives message "css3 document not known @ directive". why this?

if read mdn docs

initially in css conditional rules module level 3, @document has been postponed level 4.

so not supported in css3 yet. can expect in css4.

the @document at-rule supported in firefox prefixed -moz- prefix (@-moz-document).

JVParth