暂时使用JS和CSS翻转网站

As a December 28th joke, I would like to temporarily flip my webpage upside down with this code:

body {
transform:rotate(180deg);
-ms-transform:rotate(180deg);
-webkit-transform:rotate(180deg);
}

and I want to put this code javascript for time:

window.setTimeout(function(){ },3000);

How I can adapt the css code?

You can use a class, add the class to the body to perform the transform then remove it after

body.transform {
  transform:rotate(180deg);
  -ms-transform:rotate(180deg);
  -webkit-transform:rotate(180deg);
}

document.body.className = 'transform';
setTimeout(function(){ document.body.className = ''; },3000);