.modal {
    display: none; 
    position: fixed; 
    z-index: 11; 
    left: 0;
    top: 0;
    width: 100%; 
    height: 100%; 
    overflow: auto; 
    background-color: rgba(0,0,0,0.8); 
}

.modal-contenido {
    background-color: #fefefe;
    margin: 5% auto;
    padding: 20px;
    border: 1px solid #888;
    width: 40%;
    -webkit-transition: opacity 400ms ease-in;
    -moz-transition: opacity 400ms ease-in;
    transition: opacity 400ms ease-in;
}
@media only screen and (max-width:900px) {
    .modal-contenido {
        width: 70%;
    }
}
@media only screen and (max-width: 650px) {
    .modal-contenido {
        width: 90%;
    }
}
@media only screen and (max-width: 350px) {
    .modal-contenido {
        width: 90%;
    }
}
.cerrar {
    color: #aaa;
    float: right;
    font-size: 28px;
    font-weight: bold;
}

.close:hover,
.close:focus {
    color: black;
    text-decoration: none;
    cursor: pointer;
}