Question: I'm changing my background-image css property using Mootools:

**$(document.body).setStyle('background-image','url(' + pBackground + ')');**

*And it's its working, but how can a make one fade effect between picture change?*

Thanks,
Pedro

Answer: 
You can't fade a background specifically... you have to fade the element that has the background.

For your situation, I would suggest using a `<div>` that encompasses everything in the `<body>` of your HTML, ie:

```
<html>
<body>
<div id="main">

</div>
</body>

```

You could then set the background-image property of the #main div, and do something like this:

```
function backgroundChange(pBackground)
{
    var m = $('main');
    var fx = new Fx.Tween(m,{
        duration: 1500,
        onComplete: function(){ 
            m.setStyle('background-image','url(' + pBackground + ')');
            m.fade('in');
        }
    });
    fx.start('opacity',1,0);
}

```
Not sure of what i am saying, BUT since it's not a part of the html document, it's not an 'element' so javascript should not be able to work on it.

But, just an idea, and depending on how your site looks, you could try to set an opacity, to simulate an opacity on the body, which can lead to the effect you want..