function checkBrowserName(name){  
	var agent = navigator.userAgent.toLowerCase();  
	if (agent.indexOf(name.toLowerCase())>-1) {  
	return true;  
	}  
	return false;  
}

function fenster_anpassen(){
	if(checkBrowserName('MSIE')){
		if(Math.round(((document.body.offsetWidth-document.getElementById('page_margins').offsetWidth)/2)+3) >= 0){
			document.getElementById('bg_right').style.width=Math.round(((document.documentElement.clientWidth-document.getElementById('page_margins').offsetWidth)/2)+3)+'px';
		}else{
			document.getElementById('bg_right').style.width='0px';
		}
		document.getElementById('bg_right').style.right='-1px';
	}else{
		document.getElementById('bg_right').style.width=((document.documentElement.clientWidth-document.getElementById('page_margins').offsetWidth)/2)+3+'px';
		document.getElementById('bg_right').style.right='0px';
	}
}

window.onresize = fenster_anpassen;