样式优先级：默认样式<标签选择器<类选择器<id选择器<行内样式<!important
<!DOCTYPE html><html><head> ???<meta charset="utf-8" /> ???<title></title> ???<style> ???????#main { ???????????font-size: 80px; ???????????color: blue; ???????} ???????.box { ???????????font-size: 40px !important; ???????????color: yellow; ???????} ???????div{ ???????????font-size:20px; ???????????color:red; ???????} ?????????</style></head><body> ???<div class="box" id="main" style="font-size:120px;color:gray">哈哈</div></body></html>注释：上述代码为了屏蔽样式的层叠性，样式表都是反浏览器渲染的过程书写的，最后还是以标注了!important的标签选择器为为主。
CSS——优先级
原文地址：http://www.cnblogs.com/wuqiuxue/p/7771556.html