@keyframes flechas {
    0% {
        transform: translateY(0px);
    }
    30% {
        transform: translateY(0px);
    }

    60% {
        transform: translateY(20px);
    }
    100% {
        transform:translateY(0px);
    }
}

.mover_flecha{
    animation-name: flechas;
    animation-duration: 2s;
    animation-fill-mode: both;
    animation-iteration-count: infinite;
}