http://www.w3.org/html/ig/zh/wiki/Css3-flexbox
https://developer.mozilla.org/zh-CN/docs/CSS/CSS_Reference
http://www.poluoluo.com/jzxy/201208/173719.html
http://school.cnd8.com/css/jiaocheng/85692.htm
http://sd.csdn.net/index.php?c=page&m=subject&name=article&arcid=2808582