I put that at the end to show the long equivalent, also it doesn't set all margins to 0; 'margin 0 auto;' sets top and bottom to 0 and left auto (and possibly right auto i cant remember if it does or not)

If you want a different margin top/bottom this does the trick and should still be centred:

margin: <top value> auto <bottom value>;

__________________
mysql> SELECT * FROM `users` WHERE `users`.`clue` > 0;
Empty set (0.00 sec)