body {
  margin: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  height: 100vh;
  background-color: lightslategray;
}

.container {
  background-color: lightgray;
  width: 20rem;
}

.display input {
  width: 19rem;
  height: 6rem;
  font-family: monospace;
  font-size: xx-large;
  font-weight: bold;
  color: white;
  background-color: black;
  border: solid 2.5px lightgoldenrodyellow;
  margin-bottom: 10px;
}

div input {
  width: 4.5rem;
  height: 3.5rem;
  font-family: monospace;
  font-size: xx-large;
  font-weight: bold;
  color: white;
  background-color: lightsalmon;
  border: solid 3px lightgoldenrodyellow;
  margin: 2.5px;
}