弹出层遮罩

在点击页面按钮的时候，给弹出层的div添加此样式
.showDiv {

    background:
rgba(0, 0, 0, 0) radial-gradient(ellipse at center center , rgba(0, 0, 0, 0) 0px, rgba(0, 0, 0, 0.65) 100%) repeat scroll 0 0;
    height:
100%;
    left:
0;
    overflow:
auto;
    position:
fixed;
    top:
0;
    width:
100%;
    z-index:
101;

}