body {
  font-family: Arial, sans-serif;
  background: #f5f7fb;
  margin: 0;
  min-height: 100vh;
  display: grid;
  place-items: center;
}
.card {
  background: white;
  padding: 2rem;
  border-radius: 16px;
  box-shadow: 0 8px 24px rgba(0,0,0,0.08);
  width: min(420px, 90vw);
}
input, button {
  padding: 0.7rem;
  margin-top: 0.5rem;
}
input {
  width: 100%;
  box-sizing: border-box;
}
button {
  cursor: pointer;
}
.result {
  background: #eef7ee;
  padding: 0.75rem;
  border-radius: 8px;
}