#small #mark{
    width: 100px;
    height: 100px;
    background-color: white;
    opacity: 0.5;
    position: absolute;
    /* float: left; */
    left: 0;
    top: 0;
    /* z-index: 99; */
}
#big{
    width: 400px;
    height: 365px;
    border: 1px solid #000;
    position: absolute;
    left: 400px;
    top: 100px;
    overflow: hidden;
}
#big img{
    width: 750px;
    height: 1095px;
    position: absolute;
}