Webmaster in a Nutshell, 3rd Edition By Robert Eckstein, Stephen Spainhour
Table of Contents
Chapter 9. Cascading Style Sheets
background-position
background-position: percent
Sets the initial position of the element's background image, if specified; values are normally paired to provide x, y positions . Default position is 0% 0%. Accepted values: length , percent , top, center, bottom, left, right.