base.css  设置各种默认值：
html, body, div, span, applet, object, iframe, h1, h2, h3, h4, h5, h6, p, blockquote, pre, a, abbr, acronym, address, big, cite, code, del, dfn, em, font, img, ins, kbd, q, s, samp, small, strike, strong, sub, sup, tt, var, b, u, i, center, dl, dt, dd, ol, ul, li, fieldset, form, label, legend, table, caption, tbody, tfoot, thead, tr, th, td{margin:0;padding:0;border:0;outline:0;font-size:100%;vertical-align:baseline;background:transparent;list-style:none; }body{line-height:1; }ol, ul{list-style:none; }blockquote, q{quotes:none; }blockquote:before, blockquote:after, q:before, q:after{content:'';content:none; }:focus{outline:0; }ins{text-decoration:none; }del{text-decoration:line-through; }table{border-collapse:collapse;border-spacing:0; }.clearfix:after{content:".";display:block;height:0;clear:both;visibility:hidden; } .clear {clear: both;}*{ margin: 0; padding:0;}img{ width: 100%; display: block;}a {text-decoration: none; color: #000; -webkit-tap-highlight-color: rgba(0, 0, 0, 0);-webkit-tap-highlight-color: transparent;}section {width: 100%;height: auto;min-height: 100%;max-width: 640px; min-width:320px;margin:0 auto;padding: 0;position: relative;background: #f8f1e9;}

body{color:#000;background-color: #FFF;padding:0px; margin:0px auto;overflow:scroll;overflow-x:hidden;overflow-y:auto; font-family: Microsoft YaHei,Helvitica,Verdana,Tohoma,Arial,san-serif; font-size: 14px;font-size: 1em; font-size: 87.5%; max-width:640px;}

/*头部*/

.header {}.header .h_top{}

/*尾部*/

.footer{}.footer p{}.footer p span{}

index.css：功能模块/***************************/
.row-1{}.row-1 .r1_top{}.row-1 .r1_left{}/***************************/
.row-2{}.row-2 .r2_left{}.row-2 .box{}.row-2 .login{}/***************************/
.login{}.login .l_left{}.login .l_right{}/***************************/

<linkrel="stylesheet"type="text/css"href="css/base.css"/>   <!-- 公共样式 -->
<linkrel="stylesheet"type="text/css"href="css/index.css"/> <!-- 功能模块样式-->

<linkrel="stylesheet"type="text/css"href="css/base.css"/>   <!--公共样式-->
<linkrel="stylesheet"type="text/css"href="css/login.css"/>  <!--功能模块样式-->

<linkrel="stylesheet"type="text/css"href="css/base.css"/>   <!--公共样式-->
<linkrel="stylesheet"type="text/css"href="css/selector.css"/>  <!--功能模块样式-->

按照功能模块把css  js区分开。