.container {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  height: 100vh;
}

#display {
  font-size: 6em;
  margin: 1em 0;
}

button {
  font-size: 1.5em;
  padding: 0.5em 1em;
  margin: 0.5em;
}