语法：
<media_query_list>：[<media_query>[‘,‘ <media_query>]*]?
<media_query>：[only | not]? <media_type> [and <expression>]* | <expression> [and <expression>]*
<expression>：‘(‘<media_feature>[:<value>]?‘)‘
原文：http://www.cnblogs.com/dengxinxia/p/7069137.html