CSS: Background position y

I want to change the y background position without having to define the x background position.

Neither of these work:
background-position-y: -20px;
background-position: , -20px !important;

#menuSide a.link1 em {
 background: transparent url(/1.png) no-repeat scroll -100px 0;
#menuSide a.link2 em {
 background: transparent url(/1.png) no-repeat scroll -200px 0;
#menuSide a.link3 em {
 background: transparent url(/1.png) no-repeat scroll -300px 0;

#menuSide a:hover em {
 background-position-y: -20px !important;

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Dave BaldwinFixer of ProblemsCommented:
If you don't specify the x-position, it will be 50%.  http://www.w3schools.com/css/pr_background-position.asp  There is no way to change or specify Only the y-position because the default will be assumed for the x-position.
If you are having to use negative BG positioning in a vertical sense, there are problems in other parts of the CSS code.  Fix those problems first, before you try to second-adjust for them here, and you will likely not even have this problem.
Gurvinder Pal SinghCommented:
what do you get when you do


you can extract xpos from it and then create new value with updated ypos.

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