function center(el, x, y) {
    var p = el.parentNode, s = el.style;
    var l = ((p.offsetWidth - el.offsetWidth)/2) - sz(p,'borderLeftWidth');
    var t = ((p.offsetHeight - el.offsetHeight)/2) - sz(p,'borderTopWidth');
    if (x) s.left = l > 0 ? (l+'px') : '0';