/*使图片在浏览器中居中显示*/
.bigImg {
    position: absolute;
    top: 50%;
    left: 50%;
    width: 100%;
    /*图片向左移动自身宽度的50%, 向上移动自身高度的50%。*/
    transform: translate(-50%,-50%);
}
/*遮罩层*/
.opacityBottom {
    width: 100%;
    height: 200%;
    position: fixed;
    background: rgba(0,0,0,0.6);
    /*background: #000;*/
    z-index: 99999;
    top: -50%;
    left: 0;
}