#goTopBtn {
    display: none; /* 默认隐藏 */
    position: fixed;
    bottom: 110px;
    right: 10px;
    z-index: 99;
    border: none;
    outline: none;
    background: url(../images/gotop.png);
    cursor: pointer;
    padding: 15px;
    padding-bottom: 15px;
    width: 37px;
    height:31px;
    border-radius: 3px; /* 圆角 */
}
 
#goTopBtn:hover {
    background-color: #555; 
}