The one CTA button used across the product page -- "Jetzt kaufen", "In den Warenkorb", "Kompatibilitat prufen", "Upgrade wahlen".

```jsx
<Button variant="primary" size="lg">Jetzt kaufen</Button>
```

Variants: primary (solid brand blue, default), secondary (white + border), ghost (text-only), onNavy (light lavender-on-navy, for CTAs sitting on the solid-navy Premium card). Sizes: md, lg. Supports icon, disabled, fullWidth.