.content {
  max-width: 1200px;
  margin: auto;
  padding: 20px;
}

nav a {
  font-size: larger;
}


@media only screen and (max-width: 640px) {
  /* For mobile phones: */
  header, .column {
    flex-direction: column;
  }

  .col-half, .col-third {
    width: 90%;
  }
  nav a {
    font-size: smaller;
  }
}