1 // change background color for specific id ..
2function changebackground(){
3	document.getElementById('id').style.backgroundColor = 'green' ; 
4}
5// change background color for whole body..
6function changebackground(){
7	document.body.style.backgroundColor = 'green';
8}
9 

1document.body.style.backgroundColor = "yellow";

1function changeBackground(color) {
2   document.body.style.background = color;
3}
4
5window.addEventListener("load",function() { changeBackground('red') });

1function btn() {
2        event.stopPropagation();
3      }
4
5      var button = document.getElementById("btn");
6      button.addEventListener("click", function (e) {
7        e.target.style.backgroundColor = "green";
8      });
9      button.addEventListener("focusout", function (e) {
10        e.target.style.backgroundColor = "";
11      });