/*If you want to align center on left attribute.
The same thing is for top alignment, you could use margin-top: (width/2 of your div), the concept is the same of left attribute.
It's important to set header element to position:relative.
try this: */
#logo {
background:red;
height:50px;
position:absolute;
width:50px;
left:50%;
margin-left:-25px;
}
/* http://jsfiddle.net/DeTJH/2/
If you would like to not use calculations you can do this: */
#logo {
background:red;
width:50px;
height:50px;
position:absolute;
left: 0;
right: 0;
margin: 0 auto;
}
/* http://jsfiddle.net/DeTJH/149/ */