function threeColumn() {
	var box = document.getElementById('box');
	var shadow_left = document.getElementById('shadow_left');
	var shadow_right = document.getElementById('shadow_right');

	box.style.height = 'auto';
	var y = box.offsetHeight;

	shadow_left.style.height = y + "px";
	shadow_right.style.height = y + "px";
}