<div>W3TR</div>

div {
    width: 100px;
    height: 100px;
    background: green;
     color: white;
      position: relative;
    -webkit-animation: mymove 5s infinite; /* Chrome, Safari, Opera */
    animation: mymove 5s infinite;
    -webkit-animation-direction: alternate; /* Chrome, Safari, Opera */
    animation-direction: alternate;
}
/* Chrome, Safari, Opera */
@-webkit-keyframes mymove {
    from {top: 0px;}
    to {top: 200px;}
}

@keyframes mymove {
    from {top: 0px;}
    to {top: 200px;}
}