#glass{
    width: 42px;
    height: 38px;
    border: 1px solid #dfdfdf;
    position: absolute;
    background:url(../images/z-hear-search.png) no-repeat center;
    background-color: #fff;
}

#glass:hover
{
    /*color: #fff;*/
    border:1px solid #1e88e5;
    background:url(../images/z-hear-searchange.png) no-repeat center;
    background-color: #1e88e5;

}

hover 切换背景图片路径