message: update core concepts formatting
diff: -# Core concepts
  +---
  +title: Core Concepts
  +---
  This document aims to discuss some of the core concepts of building with Primer Components.
  @@ -50,7 +52,7 @@ We categorize our components into 3 general types. Building block components, pa
  For example, say you are using a `Button` component, and you really need to apply `Flex` styles to it. You can compose `Flex` and `Button` like so:
  - ```jsx live
  + ```.jsx
  <Flex as={Button} href='https://github.com'>Hello</Flex>
  ```
  @@ -60,7 +62,7 @@ We categorize our components into 3 general types. Building block components, pa
  For these reasons, **we recommend only using the `as` prop when you cannot achieve the same result by nesting components.** The `Flex` / `Button` example could be done like so:
  -```jsx live
  +```.jsx
  <Flex>
  <Button href='https://github.com'>Hi</Button>
  </Flex>
  