if (screen.width < 800)  
{  
	document.write('<link rel="stylesheet" type="text/css" href="css/800.css">');
}
if ((screen.width >=800)&&(screen.width <= 1024))  
{  
	document.write('<link rel="stylesheet" type="text/css" href="css/1024.css">');
}
if (screen.width >= 1025) 
{  
	document.write('<link rel="stylesheet" type="text/css" href="css/style.css">');
}