For HTML documents, however, we recommend that authors specify the background for the BODY element rather than the HTML element. If the resulting value is 'transparent', the rendering is undefined. My background is marble. When setting a background image, authors should also specify a background color that will be used when the image is unavailable. When the image is available, it is rendered on top of the background color.
All tiling covers the content and padding areas of a box.
The image is repeated horizontally only. The image is repeated vertically only. One copy of the background image is centered, and other copies are put above and below it to make a vertical band behind the element. Even if the image is fixed, it is still only visible when it is in the background or padding area of the element. However, it is recommended they interpret 'fixed' correctly, at least for the HTML and BODY elements, since there is no way for an author to provide an image only for those browsers that support 'fixed'.