@keyframes animacao {
    0% { margin-left: 0; }
    20% { margin-left: 0; }
    25% { margin-left: -100%; }
    45% { margin-left: -100%; }
    50% { margin-left: -200%; }
    70% { margin-left: -200%; }
    75% { margin-left: -300%; }
    95% { margin-left: -300%; }
    100% { margin-left: -400%; }
}