body { margin:0; overflow:hidden; font-family:sans-serif; }
#ui {
  position:fixed;
  top:10px;
  left:10px;
  background:rgba(0,0,0,0.5);
  color:white;
  padding:8px;
  border-radius:6px;
  z-index:10;
}
button {
  position:fixed;
  top:150px;
  left:10px;
  padding:6px 10px;
  margin-top:5px;
  z-index:10;
}