`<CardSubtitle />` component example:

```js
import {
  Card,
  CardBlock,
  CardTitle,
  CardSubtitle,
} from '$PACKAGE_NAME';

<Card width="50%">
  <CardBlock>
    <CardTitle>Card title</CardTitle>
    <CardSubtitle>Card subtitle</CardSubtitle>
  </CardBlock>
</Card>
```