#pop-up {
    animation-name: animacao;
    animation-duration: 1s;
    position: relative;
    animation-fill-mode: forwards;
}

@keyframes animacao {

    0% {
        top: 0px;
        left: 45%;
        opacity: 0;
    }

    100% {
        top: 200px;
        left: 45%;
        animation-duration: var(800px);
    }