body {
  background-color: #f0f2f5;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  font-family: Arial, sans-serif;
}

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

#display {
  background: #222;
  color: #0ff;
  font-size: 2em;
  text-align: right;
  padding: 15px;
  border-radius: 10px;
  margin-bottom: 15px;
  overflow-x: auto;
}

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

button {
  padding: 15px;
  font-size: 1.2em;
  border: none;
  border-radius: 10px;
  background: #e0e0e0;
  cursor: pointer;
  transition: 0.2s;
}

button:hover {
  background: #d0d0d0;
}

button.equals {
  background-color: #007bff;
  color: white;
  grid-row: span 2;
}

button.equals:hover {
  background-color: #0056b3;
}

button.zero {
  grid-column: span 2;
}