function getWindowHeight() {
  var myHeight = 0;
  if( typeof( window.innerHeigth ) == 'number' ) {
    //Non-IE
    myHeight = window.innerHeight;
  } else if( document.documentElement &&
      ( document.documentElement.clientHeight ) ) {
    //IE 6+ in 'standards compliant mode'
    myWidth = document.documentElement.clientWidth;
    myHeight = document.documentElement.clientHeight;
  } else if( document.body && ( document.body.clientHeight ) ) {
    //IE 4 compatible
    myHeight = document.body.clientHeight;
  }

  return myHeight;
}

function getWindowWidth() {
  var myWidth = 0;
  if( typeof( window.innerWidth ) == 'number' ) {
    //Non-IE
    myWidth = window.innerWidth;
  } else if( document.documentElement &&
      ( document.documentElement.clientWidth) ) {
    //IE 6+ in 'standards compliant mode'
    myWidth = document.documentElement.clientWidth;
  } else if( document.body && ( document.body.clientWidth) ) {
    //IE 4 compatible
    myWidth = document.body.clientWidth;
  }
  return myWidth;
}

function doFunc(){
if (((getWindowWidth()/2)-219)<165){
document.getElementById("mensaje").style.left=165+"px";
}else{
document.getElementById("mensaje").style.left=((getWindowWidth()/2)-219)+"px";
}
//if (((getWindowHeight()/2)-180)<200){
//document.getElementById("mensaje").style.top=200+"px";
//}else{
//document.getElementById("mensaje").style.top=((getWindowHeight()/2)-180)+"px";
//}
}
window.onresize = doFunc;