function close_submenus(){
		var ueber_sub = document.getElementById('ueber_sub');
		var kontakt_sub = document.getElementById('kontakt_sub');
		var leistungen_sub = document.getElementById('leistungen_sub');
		ueber_sub.style.display = 'none';
		kontakt_sub.style.display = 'none';
		leistungen_sub.style.display = 'none';
	}
	
	function open_submenu(id){
		var submenu = document.getElementById(id);
		close_submenus();
		if (submenu.style.display == 'none' || submenu.style.display == ''){
			submenu.style.display = 'block';
		}
		else{
			submenu.style.display = 'none';
		}
		
	}