var winW = 630, winH = 460;

function getWindowDimensions() {
  if (parseInt(navigator.appVersion)>3) {
   if (navigator.appName=="Netscape") {
    winW = window.innerWidth;
    winH = window.innerHeight;
   }
   if (navigator.appName.indexOf("Microsoft")!=-1) {
    winW = document.body.offsetWidth;
    winH = document.body.offsetHeight;
   }
  }
}

function magassag(id, offset) {
	getWindowDimensions();
	var ujm = winH - offset;
	var myElem = document.getElementById(id);
	var myStyle = myElem.style;
	myStyle.height = ujm+"px";
}