.calculator {
  width: 200px;
  height: 350px;
  background-color: #f1f1f1;
  border-radius: 5px;
  text-align: center;
}

.number {
  width: 100%;
  padding: 0.5em;
  border: none;
  margin-bottom: 0.5em;
  background-color: #f9f9f9;
  outline: none;
}

.operator {
  width: 100%;
  height: 45px;
  line-height: 45px;
  border: none;
  margin: 0;
  background-color: #4CAF50;
  color: white;
  cursor: pointer;
  font-size: 1.5em;
  border-radius: 0 0 5px 5px;
}