body {
  font-family: Arial, sans-serif;
  background-color: #f4f4f4;
  text-align: center;
  padding: 40px;
}

.calculator {
  background: white;
  display: inline-block;
  padding: 30px;
  border-radius: 10px;
  box-shadow: 0 0 10px rgba(0,0,0,0.2);
}

input, select {
  margin: 10px;
  padding: 8px;
  width: 200px;
}

button {
  padding: 10px 20px;
  font-size: 16px;
  cursor: pointer;
}