#d1{
  border-radius: 80%;
  background: #555555;
  width:20px;
  height:20px;
  position: absolute;
  animation: top 1s ease-in infinite,left 1s ease-out infinite ;
}


@keyframes top
{
0% {top: 0px;}
50% {top: 100px;}
  100% {top: 0px;}
}

@keyframes left
{
0% {left: 0px;}
50% {left: 100px;}
  100% {left: 0px;}
}