遮罩css

    position: fixed;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
    overflow: hidden;
    outline: 0;
    -webkit-overflow-scrolling: touch;
    background-color: rgb(0, 0, 0);  
    filter: alpha(opacity=60);  
    background-color: rgba(0, 0, 0, 0.6); 
    z-index: 9999;