header {
  margin-top: 6rem;
  text-align: center;
}

.subtitle {
  margin: 0 auto;
  width: 60%;
}

pre {
  background-color: #F2F2F3;
  padding: 5px;
  text-align: left;
}

.main-nav li {
  display: inline-block;
  padding: 20px;
  margin: 0 20px;
}

.main-nav {
  text-align: center;
}

a, a:visited, a:hover, a:active {
  text-decoration: none;
  color: #15AD21;
}

.side-nav {
  background-color: #F2F2F3;
}