This diagram illustrates how a background image may be repeated within the content and padding areas of a box.
In this example, a background image is first centered within a box (established by the BODY element of the example). The box contains paragraphs of text, shown in gray to make them discrete.
The image, a blue wavy line on a pale yellow background, is then repeated vertically, to the top and bottom of the BODY box. The effect is to create a wavy band down the center of the page.