body {
  font-family: system-ui, sans-serif;
  max-width: 720px;
  margin: 2em auto;
  padding: 0 1em;
  color: #222;
}

header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  border-bottom: 1px solid #ddd;
  padding-bottom: .5em;
}

nav a {
  margin-left: 1em;
  text-decoration: none;
  color: #0066cc;
}
nav a:hover { text-decoration: underline; }

footer {
  margin-top: 3em;
  text-align: center;
  font-size: .9em;
  color: #666;
}