body {
  font-family: 'Arial', sans-serif;
  background: #f6f6fc;
  text-align: center;
  padding: 40px;
}
#result {
  font-size: 1.2em;
  margin: 16px;
}
input[type="number"] {
  padding: 8px;
  font-size: 1em;
  width: 80px;
}
button {
  padding: 8px 16px;
  font-size: 1em;
  margin-left: 8px;
}
.box {
  background: #e0e7ff;
  padding: 24px;
  border-radius: 8px;
  display: inline-block;
}