html {
    font-size: 12pt;
}

@media (min-width: 640px) {
    html {
        font-size: 16pt;
    }
}

@media (min-width:640px) {
    .two-columns-example {

        display: flex;
        .two-columns-example > * {
            width: 50%;
        }
    }
}

img { 
    max-width: 100%; }

body {
    margin-left:auto;
    margin-right: auto;
    width:90%;
    max-width: 40rem;
}