javascript - jQuery - Minus percentage from CSS pixel value

Question

I'm trying to get a bunch of background-position-y values from a number of elements and minus a percentage from the pixel value and then assign that new value to each element. E.g. Minus 30% of 40px = 28px. My code below is not working as expected.

var jq = jQuery;
var icon = jq('#weather i');
jq(icon).each(function(){
    var bgPosX = jq(this).css('background-position-x');
    var bgPosY = jq(this).css('background-position-y');
    var bgPosYNew = bgPosY - 30%;
    jq(this).css({
        'background-position-x' : bgPosX,
        'background-position-y' : bgPosYNew
    });
});

Answer 1

Try the shortz:

jq(this).css('background-position-x','-=30%');

or as Klaus said:

jq(this).css('background-position-x','*=.7');

If you go DRY try this:

jQuery(this).css({backgroundPositionX:'*=.7', backgroundPositionY:'*=.7'});