img {
    max-width: 100%;
}

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

html { font-size: 12pt; }
    @media (min-width: 640px) {
        html { font-size: 16pt;}
        .two-columns-example { display: flex;}
        .two-columns-example > * { width: 50%;}
}