body {
  font-family: sans-serif;
  margin: 0;
  padding: 2rem;
  background-color: white;
  color: black;
  transition: background 0.3s, color 0.3s;
}
body.dark {
  background-color: #111;
  color: white;
}
.container {
  max-width: 600px;
  margin: auto;
}
input, button {
  display: block;
  margin-top: 1rem;
  padding: 0.5rem;
  width: 100%;
}