body {
  margin: 3em auto;
  max-width: 920px;
  background-color: white;
  color: #221c22;
  font: 110%/1.5em sans-serif;
}

details {
  margin-bottom: 1.5em;
}

summary {
  margin-bottom: 1em;
}

details[open] {
  margin-left: 2em;
}

details[open] summary {
  margin-left: -2em;
}

summary:focus {
  outline: none;
  background-color: rgb(200, 220, 255);
}

pre,
code {
  font-size: 110%;
  background-color: rgb(240, 240, 240);
  padding: 1px;
}