.bticon {
        width: 35px;
        height: 35px;
        top:2.1px;
        border-radius: 1px;
        position: fixed;margin:0 auto;z-index:2;
        border: 1px solid #f5f5f5;
        background-size: 35px 35px;
        background-repeat: no-repeat;
        background-image: url('../picture/black.svg');
 }