https://www.w3.org/TR/selectors/#specificity-rules
具體數值的計算,官方是這么說的:
即A位指 id 選擇器,B位指 class 選擇器,C位指 Tag 選擇器 (常見情況)
https://www.cnblogs.com/lzm1989/p/5907636.html
關于CSS4
https://blog.csdn.net/qq_33649233/article/details/53147987
http://www.sohu.com/a/120917966_355135
https://juejin.im/post/5c12500f51882579520b0774