in style.css:
.page-navigation a, .page-navigation span.current, .page-navigation span.extend,
.comment-navigation a, .comment-navigation span.current, .comment-navigation span.dots{
padding: 3px 5px 4px 5px;
margin: 2px;
float: left;
}
the 'float: left;' is overwriting any attempt to center the navi.
remove the float: left;
(alternatively, depending on the way css edits are done in mystique, you may need to add this to the custom css:
.page-navigation a, .page-navigation span.current, .page-navigation span.extend,
.comment-navigation a, .comment-navigation span.current, .comment-navigation span.dots{
float: none;
}
also edit your style:
.page-navigation{
margin-left: auto ;
margin-right: auto ;
}
and add: text-align: center;