Test Case Boilerplate
Fork this way...
HTML
<div id="xxx" style="position: absolute;right: 40px;top: 0;background-color: #EEE;width: 400px;height: inherit;">PRUEBA</div>
JavaScript
$('#xxx').animate({'left': '50%'}, 1000);
<div id="xxx" style="position: absolute;right: 40px;top: 0;background-color: #EEE;width: 400px;height: inherit;">PRUEBA</div>
$('#xxx').animate({'left': '50%'}, 1000);