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

.calculator {
  background: white;
  padding: 20px;
  border-radius: 10px;
  width: 260px;
}

#display {
  width: 100%;
  height: 40px;
  margin-bottom: 10px;
  font-size: 20px;
  text-align: right;
}

.buttons button {
  width: 60px;
  height: 40px;
  margin: 4px;
  font-size: 16px;
}