body{
  font-family: system-ui, -apple-system, Segoe UI, Roboto, Arial, sans-serif;
  max-width: 900px;
  margin: 0 auto;
  padding: 2rem;
}
header, footer{
  border-bottom: 1px solid #ddd;
  padding-bottom: 1rem;
  margin-bottom: 1rem;
}
footer{ border-bottom: none; padding-top: 1rem; }