body {
  font-family: system-ui, sans-serif;
  display: flex;
  justify-content: center;
  padding-top: 20vh;
  background: #f5f5f5;
  color: #222;
}

main {
  text-align: center;
  max-width: 320px;
}

#activate {
  font-size: 1.2rem;
  padding: 0.75rem 2rem;
  margin-top: 1rem;
  border: none;
  border-radius: 8px;
  background: #2e7d32;
  color: white;
  cursor: pointer;
}

#activate:disabled {
  background: #999;
  cursor: default;
}