body {
  font-family: Open Sans, Arial;
  color: #454545;
  font-size: 16px;
  margin: 2em auto;
  padding: 1em;
  max-width: 850px;
}

h1 {
  text-align: center;
}

nav > ul > li {
  display: inline-block;
  vertical-align: middle;
  padding-right: 1em;
}

.external-link {
  width: 0.7em;
  padding-left: 0.2em;
  vertical-align: top;
}

a {
  color: #14729b;
}

#main-subtitle {
  text-align: center;
  margin-top: -1em;
  margin-bottom: 2em;
}

details>summary {
  list-style: none;
}

summary::-webkit-details-marker {
  display: none
}

summary::after {
  content: ' ►';
  font-size:x-large;
}

details[open] summary:after {
  content: " ▼";
}