.nt-fix-bottom-center{
position:absolute;
bottom:0;
margin-left: auto;
margin-right: auto;
/* the following 2 lines vary 
FireFox, IE8, Safari, Chrome, Opera : yes, required
IE7 : no, must be suppressed
IE6 : doesn't work either way.
*/
left:0;
right:0; 
}

.nt-fix-top-center{
position:absolute;
top:0;
margin-left: auto;
margin-right: auto;
/* the following 2 lines vary 
FireFox, IE8, Safari, Chrome, Opera : yes, required
IE7 : no, must be suppressed
IE6 : doesn't work either way.
*/
left:0;
right:0; 
}

.nt-fix-center{
position:relative;
margin-left: auto;
margin-right: auto;
/* the following 2 lines vary 
FireFox, IE8, Safari, Chrome, Opera : yes, required
IE7 : no, must be suppressed
IE6 : doesn't work either way.
*/
left:0;
right:0; 
}