HTML:
<div class="parent">
<div class="child">
Content here
</div>
</div>

CSS:
.parent{
position:fixed;
bottom:0px;
width:100%; //width should be 100%
}
.child{
width:100px; //min width should give to center the div.
margin:0px auto; //here it will make center
}

http://htmlcsstutorials.blogspot.com/2009/08/center-align-div-horizontally-and.html

Center align a div horizontally and bottom of the page

css

CSS