Now, if you’re a front-end guy, you know that a background image cannot extend outside of an element. But what if you want to position that background relative to the position of an element, but outside of that element? I had the same problem…

Now, I’m a huge fan of jQuery, so I decided to go that route. Here’s what I did:

$('body')
    .css('background-position',
        $('#container').offset().left - 320 + 'px ' +
        $('#container').offset().top + 'px');

What does that do? jQuery finds the body element: $('body') and it sets the background position using .css('background-position', value). But, we need to get the position of my #container element, so we do that using $('#container').offset().left (with a 320px nudge) and $('#container').offset().top.

Put that in jQuery’s $(document).ready(function() and huzzah!

Well, what happens if you resize? Uh-oh, one more thing to do. I promise it won’t be hard though. Let’s just bring jQuery to the rescue again using $(window).bind('resize', function(). And, to keep up with DRY coding principles, we’ll pull it out into an alignBG() function, giving us:

function alignBG(){
    $('body')
        .css('background-position',
            $('#container').offset().left - 320 + 'px ' +
            $('#container').offset().top + 'px');
}

$(document).ready(function(){
    alignBG();

    $(window).bind('resize', function() {
        alignBG();
    });
}

And there you have it! That’s how you can position a background image based on a different element’s location in jQuery making sure that it’s in the right place on a resize.