if ((screen.width <= 800)) 
    {
	document.write("<style>#header{top:0;position:absolute;left:0;margin: 0em auto;	width:765px;}</style>");

	}
	else
	{
		document.write("<style>#header{top:0;position:absolute;left:0;margin: 0em auto;	width:1000px;}</style>");
	}