当我们需要将网页置灰的时候，可以通过css代码实现

body, html {
    filter: grayscale(100%)!important;
    -webkit-filter: grayscale(95%)!important;
    -moz-filter: grayscale(100%)!important;
    -ms-filter: grayscale(100%)!important;
    -o-filter: grayscale(100%)!important;
    filter: progid:DXImageTransform.Microsoft.BasicImage(grayscale=1);
    -webkit-filter: grayscale(1)!important;
}