img { max-width: 100%; height: auto; display: block; }

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

html { font-size: 12pt; }

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

  .two-columns-example {
    display: flex;
  }
  .two-columns-example > * {
    width: 50%;
    box-sizing: border-box;
    padding: 0 1rem;
  }
}