.header{height: 80px;position:fixed;top:0;left:0;z-index: 18;background-color: #fff;width: 100%; box-shadow: 0 0 1px #ccc;}

.header-wrapper{width: 1240px;margin: 0 auto;position: relative;}

.logo{margin-right: 80px;float: left;    width: 138px;
    height: 52px;
    padding-top: 18px;}


.header-nav{float: right;
    color: #989898;
    margin-top: 15px;
    height: 20px;
    line-height: 20px;
    margin-left: 10px;
    padding-top: 20px;}


.header-nav ul li{
    float: left;
    margin-left: 40px;
}
.header-nav ul li a{
    display: block;
    height: 24px;
    padding: 1px 20px;
    position: relative;
    font-size: 16px;
}
.header-nav ul li a span{
    display: block;
    position: relative;
    color: #000;
}
.header-nav ul li a span i{
    position: absolute;
    background: #000;
    width: 0;
    height: 2px;
    margin:auto;
    left: 0;
    right: 0;
    transition: 0.5s ease;
}
.a-bottom{
    bottom: -10px;
}
.header-nav ul li a:hover i{
    width: 100%;
}