body {
  font-family: Arial, sans-serif;
  background: #f2f2f2;
}

.calculator {
  border: 2px solid #333;
  border-radius: 10px;
  padding: 10px;
  background: #fff;
}

input[type="text"] {
  width: 100%;
  height: 40px;
  font-size: 18px;
  text-align: right;
  border: 1px solid #333;
  border-radius: 5px;
  padding: 5px;
}

button {
  width: 60px;
  height: 40px;
  font-size: 18px;
  margin: 5px;
  border: none;
  border-radius: 5px;
  background: #ddd;
  cursor: not-allowed; /* Since HTML-only, buttons are not functional */
}