.caixa {
    border: 1px solid black;
    border-radius: 10px;
    padding: 20px;
    background-color: lightgray;
}











/* ======= Responsive/Responsividade ======= */
@media (max-width: 991px){

    html {
        font-size: 55%;
    }

}

@media (max-width: 768px){


}

@media (max-width: 450px){

    html {
        font-size: 50%;
    }

}