.calculator {
  max-width: 500px;
  margin: 0 auto;
}

.calculator .controls {
  display: flex;
  flex-direction: row;
}

.calculator .methods {
  display: flex;
  flex-direction: column;
}

.calculator button {
  margin: 3px;
  height: 3em;
  width: 3em;
}