body {
  font-family: Arial, Helvetica, sans-serif;
}


nav {
  float: left;
  width: 30%;
  height: 620px;
  background: #ccc;
  padding: 20px;
}


nav ul {
  list-style-type: none;
  padding: 0;
}

article {
  float: left;
  padding: 20px;
  width: 70%;
  background-color: #f1f1f1;
  height: 620px; 
}


section::after {
  content: "";
  display: table;
  clear: both;
}


}