CSS之BFC详解

http://www.cnblogs.com/lhb25/p/inside-block-formatting-ontext.html

http://justcoding.iteye.com/blog/2314676

https://blog.csdn.net/lenLch/article/details/73090515

http://blog.sina.com.cn/s/blog_601b97ee0101b94c.html

这篇文章是我看了以后彻底明白的、并且margin合并也就彻底明白了