body {
  font-family: Arial;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  margin: 0;
  background: url('back.jpg') no-repeat center center fixed;
  background-size: cover;
}

.calc {
  background: rgba(255, 255, 255, 0.9);
  padding: 50px;
  border-radius: 15px;
  text-align: center;
  box-shadow: 0 0 10px #444;
}

input, select, button {
  margin: 5px;
  padding: 8px;
  width: 150px;
}

button {
  background: green;
  color: white;
  border: none;
  cursor: pointer;
}