@media only screen and (max-width: 400px) {

    body {
        font-size: 5px;
    }

    .box {
        width: 100%;
        min-height: 100vh;

    }

}

@media only screen and (min-width: 400px)and (max-width: 500px) {

    body {
        font-size: 8px;
    }

    .box {
        width: 400px;
    }
}

@media only screen and (min-width: 500px) {

    body {
        font-size: 10px;
    }

    .box {
        width: 25rem;
    }
}

body,
html {
    padding: 0px;
    margin: 0px;
}