Padding list

[saynogo9999]

There are a difference:

            element.addEvent('mouseleave', function(){
                fx.start({
                    'margin-left': 0,
                    'background': 'url(http://www.saynogo.com/images/tabs.jpg) no-repeat top left',
                });

            element.addEvent('mouseleave', function(){
                fx.start({
                    'margin-left': 0,
                    'background': 'url(http://www.saynogo.com/images/tabs.jpg) no-repeat top right',
                });

[Snookerman]

If that is all you want to do, you can accomplish that with css:

    #idList {
        margin: 0;
        padding: 0;
    } #idList li {
        display: block;
        margin: 0;
        padding: 4px;
        width: 120px;
        background: #333;
        color: #888;
        background: url(http://www.saynogo.com/images/tabs.jpg) right;
    } #idList li:hover {
        background-position: left;
    }

[saynogo9999]

Yes that's what i want but i wolud like to add the fade effect on hover.

[Snookerman]

I don't think MooTools can do that, you might have to find a plugin. Google "mootools plugings", here are a few sites I found:
http://www.katodivaihe.com/index.php/mootools-plugins/
http://www.visual-blast.com/javascript/mootools-plugins-accordion-menu-rounded-corners-slideshow/