*{ margin:0; padding:0;}
.bigdiv{ width:100px; height:100px; top:50%; left:50%; margin-top:-50px; margin-left:-50px;position:absolute;}
.yuan{ width:80px; height:80px; border-radius:50%; background:#666;animation:hehe 3s ease infinite;-webkit-animation:hehe 3s ease infinite; position:absolute; margin:auto; left:0; top:0; right:0; bottom:0}
@keyframes hehe
{
0%   {margin-top:0px; margin-left:0}
50%  {margin-top:10px; margin-left:10px}
100% {margin-top:0px; margin-left:0}
}
@-webkit-keyframes hehe
{
0%   {width:50px; height:50px; }
50%  {width:100px; height:100px; background-color:#003;}
100% {width:50px; height:50px; }
}