How to make full screen background in a web page

Question

How to make an image as background for web page, regardless of the screen size displaying this web page? I want to display it properly. How?

Answer 1

I found the reason why there is always a white boder of the background image, if I put the image in a 'div' element inside 'body'. But the image can be full screen, if I put it as background image of 'body'.

Because the default 'margin' of 'body' is not zero. After add this css, the background image can be full screen even I put it in 'div'.

body {
    margin: 0px;
}