Background positions can be controlled through CSS3.
the basic background statement is
There are ways to set the location of the image besides using background image repeats.
background-repeat:direction ; where direction can be repeat-x, repeat-y, no-repeat, or no value. The default is to repeat continuously within the window.
More advanced background features is attachment and position.
background-attachment:value where value can be scroll or or fixed. Attachment says how to afix the image not where to afix the image. Scroll allows the image to move with the page and fixed makes the image stationary.
Use background-position to tell the site where you want to position the background.
backgound-position: horizontal [vertical] where horizontal can be left right center or a number with a unit of measurement behind it for the horizontal measurement. If the vertical value is omitted it defaults to center otherwise use top, center or bottom. If a unit of measurement is used with vertical it is the measurement from the viewport.