html, body {
    width: 100%;
    height: 100%;
    margin: 0;
}

@media (max-width: 819px) {
    html {
        font-size: 90%;
    }
    .sm-hide {
        display: none !important;
    }
}

@media (min-width: 820px) {
    .sm-show {
        display: none;
    }
}

@media (max-width: 619px) {
    html {
        font-size: 80%;
    }
    .xs-hide {
        display: none;
    }
}

@media (min-width: 620px) {
    .xs-show {
        display: none;
    }
}