.modal {
    width: 100%;
    height: 100vh;
    background: rgba(0,0,0,0.8);
    position: absolute;
    top: 0;
    left: 0;
    display: flex;
    animation:  modal 2s 3s forwards;
    visibility: hidden;
    opacity: 0;
}
.contenido {
    margin: auto;
    margin-top: 0px;
    width: 70%;
    height: 30%;
    background: black;
    border-radius: 10px;
}
#cerrar {
    display: none;
}
#cerrar + label {
    position: fixed;
    color: #fff;
    font-size: 25px;
    z-index: 50;
    background: transparent;
    height: 30px;
    width: 30px;
    line-height:  20px;
    border-radius: 50%;
    right: 10px;
    cursor: pointer;
    animation:  modal 2s 3s forwards;
    visibility: hidden;
    opacity: 0;
}
#cerrar:checked + label, #cerrar:checked ~ .modal {
    display: none;
}
@keyframes modal {
100%{
    visibility: visible;
    opacity: 1;
    }
}