Background image resize

I have a html which includes body background. the imagae size is 开发者_如何学运维w: 400 and h: 300. and also i have set the this html window / browser size to 400 x 300. when i maximize the window the background image also should fit to the screen. how could i do this?

Read through the techniques here, look at the demos, and pick the one you find most suitable:

http://css-tricks.com/perfect-full-page-background-image/