matchHeights('bottom-wrapper', 'bottom');
matchHeights('bottom-wrapper', 'bottom-bg');

/**
 * arguments : strings of elements ids.
 */
function matchHeights(idSourceName, idDestinationName) {
	var idSource = document.getElementById(idSourceName);
	var idDestination = document.getElementById(idDestinationName);
	idDestination.style.height = idSource.offsetHeight + 'px';
}