css centering????? please help Options

[deejay21]

hello below is my css code on my page.. all i want to do is for the image to be center on any screen resolution... not sure how to do it..

CODE

<div class="masthead"><span></span></div>


<style>

body {margin-top: 180px; }

</style>
<style>

.masthead {width: 800px; height: 169px;
position: absolute; margin-left: 0px; left: 12%; top: 10px;
background-image:url(http://i1021.photobucket.com/Header.jpg);}


</style>

Reason for edit: Please use [codebox] tags when posting long codes. - Mike