If I remember correctly, something like:
Create a css class as:
.button: position: absolute; bottom: 1px;
attach this to the button.
And now you want to center it; this will work. Wrap the button in a div like so:
<div id="divCenter"><input type="button" value="Button" /></div>
Change the css to:
div#divCenter { position: absolute; bottom: 1px; text-align: center; width: 100%; }