img {
    position: relative;
    animation-name: float;
    animation-duration: 3s;
    animation-direction: alternate;
    animation-timing-function: linear;
    animation-iteration-count: 3;
}
@keyframes float {
    0% {
        left: 20px;
        top: 20px;
    }
    100% {
        left: 2000px;
        top: 900px;
    }
}