body {
    margin: 0;
    padding: 0;
    font-family: Arial, Helvetica, sans-serif;
    background-color: black;
    color: white;
    text-align: center;
}

.caixa {
    border: 1px solid gray;
    background-color: lightgray;
    color: black;
    width: 400px;
    margin: 50px auto;
    padding: 20px
}

.cor-fundo-caixa {
    background-color: aquamarine;
}


















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

    html {
        font-size: 55%;
    }

}

@media (max-width: 768px){


}

@media (max-width: 450px){

    html {
        font-size: 50%;
    }

}