aside {
  border-top: 1px dashed #602;
}

@media only screen and (min-width: 600px) {
  /* tablets and beyond */
  #page-body {
    display: flex;
    flex-direction: row;
  }
  
  main {
    width: 70%;
  }
  
  aside {
    width: 20%;
    border-top: none;
    
    margin-left: 0.5em;
    
    font-size: 0.8em;
  }
}