body {
  margin: 0;
  height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  background-color: rgba(0, 0, 0, 0.15);
}

#container {
  max-width: 354px;
  height: auto;
  background-color: rgba(0, 0, 0, 0.9);
  border-radius: 25px;
  overflow: hidden;
}

#display {
  width: 100%;
  font-size: 7rem;
  text-align: end;
  border: none;
  background-color: rgba(0, 0, 0, 0.9);
  color: white;
  box-sizing: border-box;
  padding-right: 24px;
}

.keys {
  padding: 15px;
}

.zero {
  width: 150px;
  border-radius: 25px;
}

button {
  width: 70px;
  height: 70px;
  border-radius: 50%;
  border: none;
  background-color: hsl(0, 0%, 20%);
  color: white;
  font-size: 2rem;
  cursor: pointer;
  margin: 0.17rem;
}

button:hover {
  background-color: hsl(0, 0%, 30%);
}

button:active {
  background-color: hsl(0, 0%, 40%);
}

.operator,
.orange {
  background-color: hsl(39, 100%, 55%);
}

.operator:hover,
.orange:hover {
  background-color: hsl(39, 100%, 65%);
}

.operator:active,
.orange:active {
  background-color: hsl(39, 100%, 75%);
}

.top-btns {
  background-color: hsl(0, 0%, 50%);
}