How to make a website black and white?

The day of mourning turns the website into a gray tone to express mourning.

method one

<style>
    html {
        filter: grayscale(100%);
        -webkit-filter: grayscale(100%);
        filter: progid:DXImageTransform.Microsoft.BasicImage(grayscale=1); /* IE滤镜 */
    }
</style>

Method Two

<style>
    body *{
        -webkit-filter: grayscale(100%); /* webkit */
        -moz-filter: grayscale(100%); /*firefox*/
        -ms-filter: grayscale(100%); /*ie9*/
        -o-filter: grayscale(100%); /*opera*/
        filter: grayscale(100%);
        filter:progid:DXImageTransform.Microsoft.BasicImage(grayscale=1); 
        filter:gray; /*ie9- */
    }
</style>