body {
  background-color: lightblue;
}

.container {
  margin: 100px auto 0;
}

.calculator {
  width: 300px;
  margin: 0 auto;
  padding: 20px;

  background-color: lightgray;
  border: 3px solid black;
}

.calculator__input {
  display: block;
  box-sizing: border-box;
  width: 296px;
  margin: 0 auto 15px;
  padding: 20px;

  font-size: 26px;
  text-align: right;

  border: 2px solid grey;
}

.calculator__buttons {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
}

.calculator__button {
  box-sizing: border-box;
  width: 70px;
  height: 60px;
  margin: 2px;

  font-size: 20px;

  border: 2px solid grey;
  outline: grey;
}

.calculator__button--big {
  box-sizing: border-box;
  width: 145px;
  padding: 10px;
}

.calculator__button:hover {
  background-color: #cfcdcd;
  cursor: pointer;
}

.calculator__button:active {
  background-color: #b6b6b6;
  cursor: pointer;
}