body {
  font-family: sans-serif;
  background: #f5f5f5;
  color: #222;
  margin: 0;
  padding: 0;
}
header {
  background: #4CAF50;
  color: white;
  padding: 1rem;
  text-align: center;
}
nav {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  background: #e0e0e0;
  padding: 1rem;
}
nav button {
  background: #2196F3;
  color: white;
  border: none;
  padding: 0.75rem 1rem;
  margin: 0.5rem;
  border-radius: 6px;
  font-size: 1rem;
  cursor: pointer;
}
nav button:hover {
  background: #0b7dda;
}
section {
  padding: 1rem;
  background: white;
  margin: 1rem;
  border-radius: 8px;
  box-shadow: 0 0 10px rgba(0,0,0,0.05);
}
footer {
  background: #4CAF50;
  color: white;
  text-align: center;
  padding: 1rem;
  margin-top: 2rem;
}