http://www.w3.org/TR/CSS21/cascade.html#inheritance
http://www.w3.org/TR/CSS21/cascade.html#cascade
http://www.w3.org/TR/CSS21/cascade.html#specificity
一张图看懂CSS cascade, specific, importance, inheritance
原文：http://www.cnblogs.com/kidsitcn/p/4847226.html