body {
  font-family: Arial, sans-serif;
  max-width: 700px;
  margin: auto;
  background: #f9f9f9;
  color: #222;
}
header {
  padding: 2em 0 1em 0;
  border-bottom: 1px solid #ddd;
}
nav a {
  margin-right: 1em;
  color: #0366d6;
  text-decoration: none;
}
footer {
  margin-top: 2em;
  padding: 1em 0;
  border-top: 1px solid #ddd;
  text-align: center;
  color: #888;
}