.content {
  max-width: 900px;
  margin: auto;
  padding: 20px;
}

header {
  flex-direction: column;
}

@media only screen and (max-width: 620px) {
  /* For mobile phones: */
  nav a {
    font-size: smaller;
  }

  .column {
    flex-direction: column;
  }

  .col-half, .col-third, .col-twothird {
    width: 90%;
  }

  .summary {
    background-color:gainsboro;
    padding-left:20px;
    padding-right:20px;
  }

  .column div:nth-of-type(1){
    order:2;
  }
}
  .column div:nth-of-type(2){
    order:1;
  }
}