nav{
    position: fixed;
    z-index: 99;
    width: 100%;
    height: 80px;
    background: rgba(255, 255, 255, 0.85);
}
nav>div{
    width: 1080px;
    height: 100%;
    margin: 0 auto;
    display: flex;
    flex-direction: row;
    flex-wrap: nowrap;
    align-items: center;
    justify-content: space-between;
}
nav .logo{
    display: block;
    width: 60px;
    height: 32px;
    flex-shrink: 0;
    flex-grow: 0;
    background-image: url('../images/logo.png');
    background-repeat: no-repeat;
    background-size: 49px 32px;
    background-position: left center;
}
nav .menu{
    display: flex;
    margin: 0;
    padding-left: 0;
    height: 100%;
    flex-direction: row;
    flex-wrap: nowrap;
    align-items: center;
}
nav .menu li{
    width: 80px;
    height: 100%;
    list-style: none;
    padding-left: 0;
    margin-left: 0;
    flex-shrink: 0;
    flex-grow: 0;
    
    text-align: center;
    font-family: Microsoft YaHei;
    font-size: 12px;
    line-height: 80px;
    font-style: normal;
    font-weight: 400;
}
nav .menu li.big{
    width: 120px;
}
nav .menu li a{
    display: block;
    position: relative;
    height: 100%;
    color: #4D4D4D;
}
nav .menu li a:hover, nav .menu li.active a{
    color: #FF9B00;
}
nav .menu li a:hover::after, nav .menu li.active a:after{
    content: '';
    position: absolute;
    left: 25%;
    bottom: 25px;
    width: 50%;
    height: 2px;
    flex-shrink: 0;
    border-radius: 20px;
    background: #FF9B00;
}
nav .login{
    margin-left: auto;
    width: 120px;
    display: flex;
    color: #8A8A8A;
    text-align: center;
    font-family: Microsoft YaHei;
    font-size: 12px;
    font-style: normal;
    font-weight: 400;
}
nav .login .sign-in{
    width: 54px;
    height: 24px;
    flex-shrink: 0;
    border-radius: 92px;
    border: 1px solid #FF9B00;
    background: rgba(217, 217, 217, 0.00);
    line-height: 24px;
    cursor: pointer;
}
nav .login .sign-in:hover{
    color: #FF9B00;
}
nav .login .register{
    width: 75px;
    height: 24px;
    flex-shrink: 0;
    line-height: 24px;
    cursor: pointer;
}
nav .login .register:hover{
    color: #FF9B00;
}