window.onload = function() {
		
		var body = document.body;
		var downSky = document.getElementsByClassName('down_cloud')[0];
		var up = document.getElementsByClassName('up_cloud')[0];
		var trees = document.getElementsByClassName('trees')[0];
		var ballons = document.getElementsByClassName('ballons')[0];

		body.onmousemove = function (e){
			e = e || window.event;
			downSky.style.backgroundPositionX = e.clientX/5 + "px";
			up.style.backgroundPositionX = -e.clientX/20 + "px";
			trees.style.backgroundPositionX = -e.clientX/10 + "px";
			ballons.style.backgroundPositionX = e.clientX/20 + "px";
		};
		
};