Pill-shaped action button in PBS Blue — the primary CTA across the brand ("Start Watching", "Donate").

```jsx
<Button variant="primary" iconLeft={<PlayIcon/>}>Start Watching</Button>
<Button variant="secondary">My List</Button>
<Button variant="ghost" size="sm">Learn more</Button>
<Button variant="inverse">Donate</Button>
```

Variants: primary (blue fill), secondary (blue outline), ghost (text-only), inverse (white on dark backgrounds). Sizes sm/md/lg. Pass `iconLeft`/`iconRight` as SVG nodes; use `as="a"` + `href` for links.