@keyframes elevateFall {

    0%,
    25%,
    75%,
    100% {
        transform: translateY(1px);
        filter: drop-shadow(0px 0px 15px rgba(0, 0, 0, .8));
    }

    50% {
        transform: translateY(-5px);
        filter: drop-shadow(0px 0px 0px rgba(0, 0, 0, .8));
    }
}

.escalier {
    animation: elevateFall infinite ease-in-out;
    transform-origin: center;
}

.e1 {
    animation-duration: 3s;
    animation-delay: 0.1s;
}

.e2 {
    animation-duration: 3s;
    animation-delay: 0.2s;
}

.e3 {
    animation-duration: 3s;
    animation-delay: 0.3s;
}

.e4 {
    animation-duration: 3s;
    animation-delay: 0.4s;
}

.e5 {
    animation-duration: 3s;
    animation-delay: 0.5s;
}

.e6 {
    animation-duration: 3s;
    animation-delay: 0.6s;
}

.e7 {
    animation-duration: 3s;
    animation-delay: 0.7s;
}