html { font-size: 12pt; }

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


img { max-width: 100%; }

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

@media (min-width: 640px) {
    .two-columns-example {
        display: flex;
    }

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