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') });

1// Change the background color to red
2document.body.style.backgroundColor = "red"; 

1var warning = document.getElementById("warning");
2  warning.style.background-color = "red";
3
4

1var element = document.body;
2element.style.backgroundColor = "blue";