*{
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body{
    background-color: #20201e;
}

        .caja{
            background-color: #6ed;
            width: 100px;
            height: 80px;
            margin: 1em;
            position: relative;
            animation-name: mover;
            animation-duration: 7s;
            animation-iteration-count: infinite;

        }

@keyframes mover{
    0% {
        background-color: #1f77be;
        left: 0%;
    }

    100% {
        background-color: #52523c;
        left: 100%;
    }
}