.parentBox {
    height: 100vh;
    width: 100%;
    display: flex;
    align-items: center;
    justify-content: center;

}
.contentBox {
    width: 120px;
    height: 20px;
    -webkit-mask: linear-gradient(90deg, #000 70%, #0000 0) 0/10%;
    background: linear-gradient(#07bf64 0 0) 0/0% no-repeat #ddd;
    animation: cartoon 5s infinite steps(12);
}

@keyframes cartoon {
    100% {
        background-size: 120%;
    }
}