.container {
  max-width: 800px;
  margin: 0 auto;
  text-align: center;
}

h1 {
  font-size: 3rem;
}

button {
  padding: 1rem;
  font-size: 1.5rem;
  background-color: #3498db;
  color: #fff;
  border: none;
  border-radius: 5px;
  margin: 1rem;
}

#upgrades {
  margin-top: 2rem;
}

#upgrades h2 {
  font-size: 2rem;
}

#upgrades li {
  list-style: none;
  margin: 1rem;
  padding: 1rem;
  background-color: #f2f2f2;
  border-radius: 5px;
  cursor: pointer;
}

#upgrades li:hover {
  background-color: #ddd;
}