function change() {
if (document.body.clientWidth > 1 && document.body.clientHeight > 1) { 
  myDiv.style.width=document.body.clientWidth
  myDiv.style.height=document.body.all["myDiv"].style.height
  myDiv.style.left=0
  myDiv.style.top=(document.body.clientHeight-480)/8
  }
}

window.onresize=change
window.onload=change