body {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  background: #111;
  font-family: Arial, sans-serif;
}

.calculator {
  background: #222;
  padding: 20px;
  border-radius: 15px;
  box-shadow: 0 0 20px rgba(255,255,255,0.2);
}

#display {
  width: 100%;
  height: 50px;
  font-size: 1.5rem;
  text-align: right;
  margin-bottom: 20px;
  padding: 10px;
  background: #000;
  color: #0f0;
  border: none;
  border-radius: 10px;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 60px);
  gap: 10px;
}

.btn {
  padding: 15px;
  font-size: 1.2rem;
  border: none;
  border-radius: 10px;
  background: #333;
  color: white;
  cursor: pointer;
}

.btn:hover {
  background: #444;
}

.operator {
  background: #f39c12;
}

.operator:hover {
  background: #e67e22;
}

.equal {
  background: #27ae60;
}

.equal:hover {
  background: #2ecc71;
}

.clear {
  grid-column: span 4;
  background: #e74c3c;
}

.clear:hover {
  background: #c0392b;
}