@media screen

参考地址：

http://www.swordair.com/blog/2010/08/431/

http://ashaochangfu.blog.163.com/blog/static/104251730201210245438273/

http://newhtml.net/通过-css-media-query-制作感知屏幕尺寸的表格/

http://www.zhangxinxu.com/wordpress/2011/08/css3-media-queries%E7%9A%84%E4%BA%9B%E9%87%8E%E5%8F%B2%E5%A4%96%E4%BC%A0/

http://webdesignerwall.com/tutorials/css3-media-queries

http://www.ruanyifeng.com/blog/2012/05/responsive_web_design.html