function cambiartamanio() {
	
	var tamanio = screen.width;
	if (tamanio<=650) {
 		setActiveStyleSheet('A');
	} else if ((tamanio>=660) && (tamanio<=900)) {
 		setActiveStyleSheet('A+');
	} else if (tamanio>=910) {
 		setActiveStyleSheet('A++');
	} else {
  		setActiveStyleSheet('A');
	}
}

function setActiveStyleSheet(title) {
  var i, a, main;
  for(i=0; (a = document.getElementsByTagName("link")[i]); i++) {
    if(a.getAttribute("rel").indexOf("style") != -1 && a.getAttribute("title")) {
      a.disabled = true;
      if(a.getAttribute("title") == title) a.disabled = false;
    }
  }
}