body {
  font-family: Arial, sans-serif;
  background-color: #f4f4f4;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  margin: 0;
}

.calculator {
  background: #222;
  padding: 20px;
  border-radius: 12px;
  box-shadow: 0 4px 15px rgba(0, 0, 0, 0.2);
  width: 300px;
}

#display {
  width: 100%;
  height: 50px;
  font-size: 24px;
  text-align: right;
  margin-bottom: 20px;
  padding: 10px;
  border: none;
  border-radius: 8px;
  background: #333;
  color: #fff;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 12px;
}

.btn {
  padding: 20px;
  font-size: 20px;
  border: none;
  border-radius: 10px;
  background-color: #444;
  color: #fff;
  cursor: pointer;
  transition: background 0.2s;
}

.btn:hover {
  background-color: #555;
}

.operator {
  background-color: #ff9500;
}

.operator:hover {
  background-color: #e08600;
}

.equal {
  background-color: #28a745;
}

.equal:hover {
  background-color: #218838;
}

.clear {
  background-color: #dc3545;
}

.clear:hover {
  background-color: #c82333;
}

.backspace {
  background-color: #6c757d;
}

.backspace:hover {
  background-color: #5a6268;
}

.function {
  background-color: #17a2b8;
}

.function:hover {
  background-color: #138496;
}