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;
        width: 50%;
    }
  }