/*header*/
.header{
    position: fixed;
    top: 0;
    left: 0;
    z-index: 10;
    width: 100%;
    height: 50px;
    background-color: #fff;
}
.nav{
    width: 100%;
}
.nav_list{
    display: flex;
    width: 94%;
    padding: 0 3%;
    line-height: 50px;
    justify-content: space-between;
}
.nav_item{
    position: relative;
    text-align: center;
}
.nav_item a{
    color: #333;
}
.nav_menu{
    display: none;
    position: absolute;
    top: 60px;
    left: calc((100% - 80px) / 2);
    width: 80px;
    line-height: 40px;
    padding: 10px 0;
    text-align: center;
    border-radius: 10px;
    background-color: #fff;
    box-shadow:-5px 5px 10px -4px #ddd,5px 5px 10px -4px #ddd;
}
.nav_menu a{
    display: inline-block;
    width: 100%;
    color: #333;
}
.nav_menu:before{
    content: ' ';
    display: inline-block;
    position: absolute;
    top: -17px;
    left: 30px;
    width: 0;
    height: 0;
    border: 10px transparent solid;
    border-bottom: 10px #fff solid;
}