function showBack2Top() {
	fromTop = (window.pageYOffset) ? window.pageYOffset : document.body.scrollTop;
	winHeight = (window.innerHeight) ? window.innerHeight : document.body.clientHeight;
	if (document.getElementById('back2top')) document.getElementById('back2top').style.display = (fromTop >= 144) ? 'block' : 'none';
}