最常用的li导航写法:
#head_r_b {width:628px;height:60px;}
...
#head_r_b ul {list-style-type:none;height:44px;margin:0;padding:16px 0 0 20px;}
#head_r_b li {width:80px;height:44px;float:left;margin-right:2px;}
#head_r_b li a {width:80px;height:44px;background:url(images/over.jpg) no-repeat;float:left;font:bold 14px "宋体";color:#fff;text-align:center;line-height:50px;}