function winwidth() {
	if (window.innerWidth)
		return window.innerWidth;
	else if (document.body && document.body.offsetWidth)
		return document.body.offsetWidth;
	return 0;
	}
function topbar() {
	if (winwidth() < 950)
		imgfile = 'none';
	else
		imgfile = 'url(i/ziegeln_quer.jpg)';
	document.getElementById("top").style.backgroundImage = imgfile;
	}
	window.onresize=topbar;