div {
    width: 100px;
    height: 100px;
    background-color: green;
    border-radius: 50%;
    position: relative;
    animation: 5s linear anim infinite alternate;
}

div:hover {
    background-color: red;
    transition: 2s;
}

@keyframes anim {
    from {
        left: 0;
    }

    to {
        left: calc(100% - 100px);
    }
  }