body {
  font-family: system-ui, -apple-system, 'Segoe UI', Roboto, 'Helvetica Neue', Arial;
  background: #f6f7fb;
  color: #222;
  margin: 0;
  padding: 2rem;
}
.container {
  max-width: 680px;
  margin: 0 auto;
  background: #fff;
  padding: 1.5rem 2rem;
  border-radius: 8px;
  box-shadow: 0 6px 18px rgba(20,30,60,0.08);
}
h1 { margin-top: 0; }
.controls { margin-top: 0.75rem; }
button { margin-right: 0.5rem; padding: 0.5rem 0.9rem; }
.result { margin-top: 1rem; font-weight: 600; }
footer { margin-top: 1.25rem; font-size: 0.9rem; color: #666 }