.img-box {
    width: 1000px;
    margin: auto;
    line-height: 0;
    background-image: url(images/background.png);
    overflow: hidden;
    position: relative;
}

.img-wrap {
    position: absolute;
    left: 0;
    top: 0;
    overflow: hidden;
    width: 20px;
}

span {
    width: 1px;
    height: 100%;
    cursor: ew-resize;
    background: #fff;
    position: absolute;
    left: 20px;
    top: 0;
}

.arrow {
    width: 40px;
    position: absolute;
    top: 50%;
    margin-left: -20px;
    margin-top: -20px;
}