body {
  font-family: Arial, sans-serif;
  max-width: 800px;
  margin: 2rem auto;
  padding: 1rem;
  line-height: 1.5;
}
h1 { color: #333; }
button {
  padding: 0.5rem 1rem;
  font-size: 1rem;
  cursor: pointer;
}
pre {
  background: #f4f4f4;
  padding: 1rem;
  white-space: pre-wrap;
}