body {
  margin: 0;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  background-color: #222;
}

#calculator {
  font-family: Arial, sans-serif;
  background-color: #333;
  padding: 20px;
  border-radius: 10px;
  width: 300px; /* Updated from 240px to allow round buttons */
}


#display {
  width: 100%;
  padding: 10px;
  font-size: 2rem;
  margin-bottom: 10px;
  background-color: #f4f4f4;
  color: #1abc9c;
  border: none;
  border-radius: 5px;
}


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

button {
  width: 60px;
  height: 60px;
  font-size: 1.5rem;
  border: none;
  border-radius: 50%; /* ← makes buttons fully round */
  background-color: #555;
  color: #fff;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
}


button:hover {
  background-color: #777;
}

.operator-btn {
  background-color: #1abc9c;
}