Please help me take a look at this_html/css_WEB-ITnose

* {
padding:0;
margin:0
}
#top {
width:100%;
height:20px;
border-bottom:solid 1px #D5D5D5;
background:url(img/top.jpg)
}
body {
background-image: url(img/body_bgck.jpg);
background-repeat: repeat-x;
}
/*网站主体*/
#main {
width:910px;
height:1024px;
border:solid 1px #71B8FF;
margin:auto;
}
/* 导航栏*/
#nav {
width:auto;
height:40px;
border: solid 1px #E9FEFC;
margin-top:80px;
}
#nav_left {
width:63px;
height:40px;
margin-left:0px;
margin-top:0px;
float:left;
background:url(img/nav_left.png) left no-repeat;
}
#nav_rigth {
width:63px;
height:40px;
margin-right:0px;
margin-top:0px;
float: right;
background:url(img/nav.png) no-repeat;
}
#nav_content {
width:785px;
height:40px;
margin:auto;
background:url(img/nav_content.png) repeat-x;
clear: none;
}
.nav_ul {
display:block;
width:100%;
height:40px;
margin-top:0;
}
.nav_li {
list-style:none;
float:left;
display: block;
padding:5px;
margin-top: 3px;
margin-right: 20px;
margin-bottom: 3px;
margin-left: 20px;
}