为什么要初始化CSS？
CSS初始化是指重设浏览器的样式。不同的浏览器默认的样式可能不尽相同，所以开发时的第一件事可能就是如何把它们统一。如果没对CSS初始化往往会出现浏览器之间的页面差异。每次新开发网站或新网页时候通过初始化CSS样式的属性，为我们将用到的CSS或html标签更加方便准确，使得我们开发网页内容时更加方便简洁，同时减少CSS代码量，节约网页下载时间。
CSS初始化示例代码
/*
css reset www.admin10000.com
*/
body,div,dl,dt,dd,ul,ol,li,h1,h2,h3,h4,h5,h6,pre,code,form,fieldset,legend,input,button,textarea,p,blockquote,th,td { margin: 0; padding: 0; }
body { background: #fff; color: #555; font-size: 14px; font-family: Verdana, Arial, Helvetica, sans-serif; }
td,th,caption { font-size: 14px; }
h1, h2, h3, h4, h5, h6 { font-weight: normal; font-size: 100%; }
address, caption, cite, code, dfn, em, strong, th, var { font-style: normal; font-weight: normal;}
a { color: #555; text-decoration: none; }
a:hover { text-decoration: underline; }
img { border: none; }
ol,ul,li { list-style: none; }
input, textarea, select, button { font: 14px Verdana,Helvetica,Arial,sans-serif; }
table { border-collapse: collapse; }
html { overflow-y: scroll;}
/* css common */
.clearfix:after { content: "."; display: block; height: 0; clear: both; visibility: hidden;}
.clearfix { *zoom: 1; }
body,div,dl,dt,dd,ul,ol,li,h1,h2,h3,h4,h5,h6,pre,code,form,fieldset,legend,input,button,textarea,p,blockquote,th,td { margin: 0; padding: 0; }
body { background: #fff; color: #555; font-size: 14px; font-family: Verdana, Arial, Helvetica, sans-serif; }
td,th,caption { font-size: 14px; }
h1, h2, h3, h4, h5, h6 { font-weight: normal; font-size: 100%; }
address, caption, cite, code, dfn, em, strong, th, var { font-style: normal; font-weight: normal;}
a { color: #555; text-decoration: none; }
a:hover { text-decoration: underline; }
img { border: none; }
ol,ul,li { list-style: none; }
input, textarea, select, button { font: 14px Verdana,Helvetica,Arial,sans-serif; }
table { border-collapse: collapse; }
html { overflow-y: scroll;}
/* css common */
.clearfix:after { content: "."; display: block; height: 0; clear: both; visibility: hidden;}
.clearfix { *zoom: 1; }