background style from external css bug?

background style from external css bug?


in main html i include .css so:
<link type="text/css" rel="stylesheet" href="my.css" />
then declare in my.css
#my {
background-position: 50% 50%
}
when i try to get style "background-position" with $
("#my").css('backgroundPosition') or $("#my").css('background-
position') i recieve just "undefined", but when i use
<div style="background-position: 50% 50%"></div> it works fine. what
the point?
ps. jquery 1.2/FF2.0.6
pps. $("#my").css('background') doesn't work too, but $
("#my").css('background-image') work.(not in this example)