img { 
    max-width: 100%; 
}

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

html { font-size: 12pt; }

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