.back-to-top {
    position: fixed;
    _position: absolute;
    float: left;
    display: none;
    right: 10px;
    bottom: 10px;
    _bottom: 0px;
    cursor: pointer;
    z-index: 9999;
    font-size: 20px;
    color: #ffffff;
    width: 30px;
    height: 30px;
    background-color: #333333;
    border-radius: 50%;
    line-height: 30px;
    text-align: center;
}