#box {
    width: 400px;
    height: 100px;
    margin: 0px auto 0;
    font:12px/180% Arial,Lucida,Verdana,"微软雅黑",Helvetica,sans-serif;
}
#tab_nav {
    margin: 0;
    padding: 0;
    height: 25px;
    line-height: 20px;  
}
#tab_nav li {
    float: left;
    margin: 0 3px;
    list-style: none;
    border: 1px solid #999;
    border-bottom: none;
    height: 24px;
    width: 60px;
    text-align: center;
    background: #FFF;
    font:12px/180% Arial,Lucida,Verdana,"宋体",Helvetica,sans-serif;
}
a {
    font: bold 14px/24px "微软雅黑", Verdana, Arial,
          Helvetica,sans-serif;
    color: green;
    text-decoration: none;
}
a:hover {
    color: red;
}
#tab_content {
    width: 550px;
    height: 450px;
    border: 1px solid #999;
    font: 12px/180% Arial,Lucida,Verdana,"微软雅黑",Helvetica,sans-serif; 
    text-align: center;
    background: #FFF;
    overflow: hidden;
}
#t_1,#t_2,#t_3,#t_4,#t_5,#t_6 {
    width: 100%;
    height: 450px;
}

.change{background:red;}