jQuery图像向上滑动而不是向右滑动

基本上，我的代码是在我希望图像向右滑动时使其向上滑动。怎么了

HTML

<div id="wrapper">
    <div id="header">
    </div>
</div>

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下面是代码：

您需要增加值

function scrollBg(){

    //Go to next pixel row.
    current += step; //increment instead of decrement

    //If at the end of the image, then go to the top.
    if (current == restartPosition){
        current = 0;
    }

    //Set the CSS of the header.
    $('#header').css("background-position",current +"px 0"); // parameters are right top not top right



}

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演示：

更新：我找到了答案

$('#header').css("background-position","0 "+current+"px");

我将0更改为1，它将其修复。这纯粹是运气使然，但为什么要这样做呢

$('#header').css("background-position","0 "+current+"px");