<div class=p></div><div style="height:300px"></div><div class=p></div><div id=b></div>0-0<style>.p{width:99px;height:20px;background:#000}*{margin:0}#b{position:absolute;background:#F00;width:20px;height:20px;animation-name:b;animation-duration:3s;animation-iteration-count:infinite;left:40px}@keyframes b{from{top:20px}50%{top:300px}to{top:20px}}</style>