Position one HTML element below another

function getRealPosition(elmnt) { // h/t to http://www.quirksmode.org/js/findpos.html
	elmnt = typeof elmnt == 'object' ? elmnt : document.getElementById(elmnt);
	elmntLeft = elmnt.offsetLeft;
	elmntTop = elmnt.offsetTop;
	while(elmnt = elmnt.offsetParent) {
		elmntLeft += elmnt.offsetLeft;
		elmntTop += elmnt.offsetTop;
	}
	return [elmntLeft, elmntTop];
}
 
function positionBelow(elmntAbove, elmntBelow, topDiff, leftDiff) {
	elmntAboveRealPosition = getRealPosition(elmntAbove);
	elmntBelow = typeof elmntBelow == 'object' ? elmntBelow : document.getElementById(elmntBelow);
	elmntBelow.style.left = elmntAboveRealPosition[0] + (leftDiff ? leftDiff : 0) + 'px';
	elmntBelow.style.top = elmntAboveRealPosition[1] + (topDiff ? topDiff : 0) + 'px';
	if(elmntBelow.style.position!='absolute')
		elmntBelow.style.position = 'absolute';
}