$(function () {

	var container = $('#night');
	var measurer = $('#measurer');

	function windowHeight() {
		var de = document.documentElement;
		return self.innerHeight || (de && de.clientHeight) || document.body.clientHeight;
	}

	function scrollY() {
		var de = document.documentElement;
		return self.pageYOffset || (de && de.scrollTop) || document.body.scrollTop;
	}

	function move(evt) {
		var left = (evt.pageX * 100 / measurer.width()) - 100;
		left = (left > 0) ? 0 : left; 
		container.css('left', left + '%');
	}

	function setTop() {
		container.css('top', windowHeight() + scrollY() + 'px');
	}

	function init() {
		container.removeClass('hidden');
		
		$(document).mousemove(function (evt) {
			move(evt);
		});
		$(window).resize(function () {
			setTop();
		});
		$(window).scroll(function () {
			setTop();
		});
	}

	init();
	setTop();

});