@media screen and (min-width: 480px) {
  
  /***************************************
  TWO COLUMN LAYOUT
  ***************************************/
  
  #primary {
    width: 50%;
    float: left;
  }
  
  #secondary {
    width: 40%;
    float: right;
  }
  
  
  
  /***************************************
  PAGE: BOOKS
  ***************************************/
  
  .books li {
    float: left;
    max-width: 45%;
    margin: 2.5%;
  }
  
  
  /***************************************
  PAGE: ABOUT
  ***************************************/
  
  .profile-photo {
    float: left;
    margin: 0 5% 80px 0;
  }
  
}

@media screen and (min-width: 660px) {
  
  
  /***************************************
  PAGE: BOOKS
  ***************************************/
  
  .books li {
    width: 28.3333%
  }
  
  .books li:nth-child(4n) {
    clear: left;
  }
  
  
  
  /***************************************
  PAGE: HEADER
  ***************************************/
  
  nav {
    background: none;
    float: right;
    font-size: 1.125em;
    text-align: right;
    width: 55%;
  }
  
  #logo {
    float: left;
    margin-left: 5%;
    text-align: left;
    width: 40%;
  }
  
  h1 {
    font-size: 2em;
  }
  
  h2 {
    font-size: 0.825em;
    margin-bottom: 20px;
  }
  
  header {
    border-bottom: 5px solid #599a68;
    margin-bottom: 60px;
  }
  
}