body {
  font-family: system-ui, sans-serif;
  background-color: #111;
  color: #eee;
  margin: 0;
  padding: 0;
}
header, section {
  padding: 80px 20px;
  max-width: 800px;
  margin: auto;
}
nav {
  background-color: #000;
  padding: 10px 20px;
  display: flex;
  justify-content: space-between;
  align-items: center;
}
nav a {
  color: #aaa;
  text-decoration: none;
  margin-left: 20px;
}
nav a:hover {
  color: #fff;
}
h1, h2 {
  color: #fff;
}
button {
  background-color: #0ff;
  border: none;
  padding: 12px 24px;
  font-size: 1rem;
  cursor: pointer;
  color: #000;
  border-radius: 5px;
}
.demo-output {
  background: #222;
  padding: 20px;
  margin-top: 20px;
  border-left: 4px solid #0ff;
  font-family: monospace;
  white-space: pre-wrap;
}
footer {
  text-align: center;
  font-size: 0.9rem;
  padding: 20px;
  color: #555;
}