body {
  font-family: Arial, sans-serif;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  background-color: #f0f0f0;
}

.calculator {
  background: white;
  padding: 30px;
  border-radius: 16px;
  box-shadow: 0 0 25px rgba(0,0,0,0.2);
  width: 360px;
}

.display {
  width: 100%;
  height: 70px;
  font-size: 36px;
  margin-bottom: 20px;
  padding: 10px;
  text-align: right;
  border: 2px solid #ccc;
  border-radius: 10px;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 15px;
}

button {
  padding: 25px;
  font-size: 24px;
  border: none;
  background: #eee;
  border-radius: 10px;
  cursor: pointer;
  transition: background 0.2s;
}

button:hover {
  background: #ddd;
}

button.operator {
  background: #f9a825;
  color: white;
}

button.operator:hover {
  background: #f57f17;
}

button.equal {
  grid-column: span 2;
  background: #43a047;
  color: white;
}

button.equal:hover {
  background: #388e3c;
}