function setActiveStyleSheet() {
   var i, a, main, largeur;

   if(screen.width<=900)
      {largeur="800"}
   else if(screen.width<=1124)
      {largeur="1024"}
   else if(screen.width<=1380)
      {largeur="1280"}
   else if(screen.width<=1780)
      {largeur="1680"}
   else
     {largeur="1920"}

   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") == largeur) a.disabled = false;
     }
   }
}