.back-box{
            position: fixed;
            max-width: 750px;
            top: 6rem;
            left: auto;
            width: 0.8rem;
            height: 0.5rem;
            border-radius: 0 0.2rem 0.2rem 0;
            background: rgba(255,255,255,0.7);
            z-index: 999;
            display: flex;
            align-items: center;
            justify-content: center;
            box-shadow: 0 0.01rem 0.03rem #ccc;
        }
.back-box img{
    width: 0.3rem;
    height: auto;
}