function calcParallax(tileheight, speedratio, scrollposition) {
	return (tileheight) - scrollposition / speedratio;
}
window.onload = function() {
	window.onscroll = function() {
		var posX = (document.documentElement.scrollLeft) ? document.documentElement.scrollLeft : window.pageXOffset;
		var posY = (document.documentElement.scrollTop) ? document.documentElement.scrollTop : window.pageYOffset;
		var ground = document.getElementById('ground');
		var groundparallax = calcParallax(0, 10, posY);
		ground.style.backgroundPosition = "0 " + groundparallax + "px";
	}
	document.getElementById('posts').onscroll = function() {
		var posX = (this.scrollLeft) ? this.scrollLeft : this.pageXOffset;
		var j = calcParallax(53, 16, posX);
		console.log('scroll js: '+ j);
		document.getElementById('javascriptcode').style.backgroundPosition = j + "px 0";
	}
}