.modal {
    width: 100%;
    height: 100vh;
    background: rgba(0,0,0,0.8);  
    position: absolute;
    top: 0;
    left: 0;  
    display: flex;
    z-index: 999;
    
    animation: modal 2s 3s forwards;
    visibility: hidden;
    opacity: 0;
}

.contenido {
    margin: auto;
    width: 350px;
    height: 350px;
    background: white;
    z-index: 999;
}

#cerrar {
    display: none;
}

#cerrar + label {
    position: absolute;
    color: #fff;
    font-size: 25px;
    z-index: 9999;
    background: red;
    height: 40px;
    width: 40px;
    line-height: 40px;
    border-radius: 50%;
    right: 150px;
    top: 40px;
    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;
    }
}