body {
    text-align: center;
    font-family: sans-serif;
    margin: 0;
}

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

.contenido {
    margin: auto;
    width: 55%;
    height: 70%;
    background: white;
    border-radius: 10px;
}

#cerrar {
    display: none;
}

#cerrar + label {
    position: fixed;
    color: #fff;
    font-size: 25px;
    z-index: 50;
    background: darkred;
    height: 40px;
    width: 140px;
    line-height: 40px;
    border-radius: 40%;
    right: 150px;
    top: 150px;
    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;
    }
}