$(document).ready( function() {
  if (screen.width <= 1024)
  {
    $("#mainTbl").css("width","980px").attr("align","center");
  }
  else if (screen.width <= 1200)
  {
    $("#mainTbl").css("width","1140px").attr("align","center");
  }
  else
  {
    $("#mainTbl").css("width","1240px").attr("align","center");
  }
});