How to make the entire web page gray

In order to commemorate the death of some influential great people or important anniversaries, it is necessary to make all web pages gray to express our condolences to the deceased.
In fact, this function is very simple. You only need to add the following code to the head tag of HTML

<style type="text/css">
html {
    
    
filter: progid:DXImageTransform.Microsoft.BasicImage(grayscale=1);
-webkit-filter: grayscale(100%);}
</style>