function flash_div(){
  var scr_width=window.screen.width;
  switch(true)
  {
    case scr_width < 1280:
	 var css=document.getElementById("css");
	 css.setAttribute("href","css/css.css"); 
	 document.getElementById("div1024").style.display='block';
	  document.getElementById("div1250").style.display='none';

  break; 
    case scr_width >= 1280:
     var css=document.getElementById("css");
     css.setAttribute("href","css/1280.css");  
	 document.getElementById("div1024").style.display='none';
	 document.getElementById("div1250").style.display='block';
  break;
  }   
}  
window.onload=function(){ 
   flash_div();
}