body {
  font-family: system-ui, sans-serif;
  margin: 0;
  background: #f5f5f5;
}

header {
  background: #1e1e1e;
  color: white;
  padding: 1rem;
}

nav button {
  margin: 0.2rem;
  padding: 0.5rem;
  cursor: pointer;
}

section {
  padding: 1rem;
}