body {
  margin: 0;
  font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
  background: linear-gradient(145deg, #ececec, #f9f9f9);
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
}

.calculator {
  background-color: #222;
  padding: 2rem;
  border-radius: 1.5rem;
  box-shadow: 0 0 30px rgba(0, 0, 0, 0.25);
  width: 300px;
}

.display {
  background-color: #000;
  color: #0f0;
  font-size: 2rem;
  text-align: right;
  padding: 1rem;
  border-radius: 0.5rem;
  margin-bottom: 1rem;
  min-height: 3rem;
  word-wrap: break-word;
}

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

.btn {
  padding: 1rem;
  font-size: 1.2rem;
  border: none;
  border-radius: 0.75rem;
  background-color: #333;
  color: #fff;
  cursor: pointer;
  transition: all 0.2s ease;
}

.btn:hover {
  background-color: #444;
}

.operator {
  background-color: #ff9500;
}

.operator:hover {
  background-color: #e68a00;
}

.equal {
  background-color: #34c759;
  grid-row: span 2;
}

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

.zero {
  grid-column: span 2;
}