Animation

And back and forth:

with another word: #inside {
position: absolute;
top: 0;
left: 0;
height: 10px;
width: 10px;
background: red;
animation: moveit 2s alternate infinite
}

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