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

#calculator {
  font-family: Arial, Helvetica, sans-serif;
  background-color: rgba(0, 0, 0, 0.624);
  border-radius: 10px;
  max-width: 500px;
  overflow: hidden;
}
#display {
  width: 100%;
  padding: 20px;
  font-size: 5rem;
  text-align: left;
  border: none;
  background-color: rgba(0, 0, 0, 0.397);
  color: white;
}

#keys {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 10px;
  padding: 25px;
}

button {
  width: 100px;
  height: 100px;
  border-radius: 30px;
  border: none;
  /* background-color: rgba(70, 255, 0, 0.500); */
  background-color: black;
  color: white;
  font-size: 3rem;
  font-weight: bold;
  cursor: pointer;
}

button:hover {
  /* background-color: rgba(70, 255, 0,0.700); */
  background-color: white;
  color: black;
  font-size: 3.5rem;
  font-weight: bolder;
}

button:active {
  
  border: 5px solid black;
}

.operator-btn {
  background-color: rgba(255, 255, 0, 0.8);
  color: black;
}

.operator-btn:hover {
  background-color: rgba(255, 255, 0, 0.9);
}
.operator-btn:active {
  background-color: rgba(255, 255, 0, 1);
}