转自：http://www.zhangxinxu.com/wordpress/2011/06/css3%E9%80%89%E6%8B%A9%E5%99%A8nth-child%E5%92%8Cnth-of-type%E4%B9%8B%E9%97%B4%E7%9A%84%E5%B7%AE%E5%BC%82/
CSS3选择器:nth-child和:nth-of-type之间的差异
原文：https://www.cnblogs.com/mengfangui/p/9132533.html
