shango420/index.html

## index.html
<input type="button" value="start countdown"  onclick="countdown(4)">

## script.js
function countdown(n) {
  while (n --> 0)
    alert(n);
  blastoff();
}

function blastoff() { document.body.className = "go"; }

## style.css
body.go {
  background: url(https://38.media.tumblr.com/c540bc0f4ed932580f3a1b3366232abc/tumblr_ncom5xy6bM1qejpvyo1_500.gif);
  background-size: cover;
}
	function countdown(n) {
	while (n --> 0)
	alert(n);
	blastoff();
	}

	function blastoff() { document.body.className = "go"; }
	body.go {
	background: url(https://38.media.tumblr.com/c540bc0f4ed932580f3a1b3366232abc/tumblr_ncom5xy6bM1qejpvyo1_500.gif);
	background-size: cover;
	}