body {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  margin: 0;
  background-color: #f0f0f0; 
}

#calculator {
  height: 400px;
  width: 1000px;
  padding: 10px 20px;
  border: 5px solid rgb(113, 113, 113);
  justify-content: center;
  width: 200px;
  background: black;
  border-radius: 5px;
  box-shadow: 0 0 10px rgba(0, 0, 0, 0.1); 
}

#display {
  font-size: 20px;
  margin: 20px 0;
  width: 95%;
  color: white;
  background-color: rgb(51, 48, 48);
  height: 10%;
  text-align: right;
}

.btn-container {
  display: flex;
  flex-wrap: wrap;
  justify-content:center;
}

.btn-upper, .btn-side, .btn-middle, .btn-lower {
  font-size: 20px;
  border-radius: 10px;
  border-color: aliceblue;
  margin-bottom: 10%;
  color: white;
  cursor: grab;
  font-weight: 500;
  text-align: center;
  margin-right: 2.5%;
  margin-left: 2.5%;
}

.btn-upper {
  height: 40px;
  width: 20%;
  background-color: rgb(117, 114, 114);
}

.btn-side {
  height: 40px;
  width: 20%;
  background-color: rgb(247, 156, 20);
}

.btn-middle {
  height: 40px;
  width: 20%;
  background-color: rgb(57, 54, 54);
}

.btn-lower {
  height: 40px;
  width: 41%;
  background-color: rgb(57, 54, 54);
}