body, html {
  background-color: #fff;
  font: 100%/1.5 Georgia, Times, serif;
}

header, main, footer {
  font-size: 120%;
  margin: 0 auto;
  max-width: 100%;
  width: 40em;
}

@media (min-width: 667px) {
  header, main, footer {
    width: 30em;
  }
}