The background shorthand property sets all the background properties in one declaration.
The properties that can be set, are: background-color, background-image, background-position, background-size, background-repeat, background-origin, background-clip, and background-attachment.
It does not matter if one of the values above are missing, e.g. background:#ff0000 url(smiley.gif); is allowed.
Note: If one of the properties in the shorthand declaration is the bg-size property, you must use a / (slash) to separate it from the bg-position property, e.g. background:url(smiley.gif) 10px 20px/50px 50px; will result in a background image, positioned 10 pixels from the left, 20 pixels from the top, and the size of the image will be 50 pixels wide and 50 pixels high.
Note: If using multiple background-image sources but also want a background-color, the background-color parameter needs to be last in the list.
background: bg-color bg-image position/bg-size bg-repeat bg-origin bg-clip bg-attachment initial|inherit;
body { background: #00ff00 url("smiley.gif") no-repeat fixed center; }