Make the embed leaderboard have the same rounded corners

https://www.patinanetwork.org/programs/codebloom

The Patina Network page showcasing Codebloom is currently in progress, but a nice thing to have would be that the POTD has a nice rounded edge but the leaderboard doesn’t. It would be nice to have this consistent rounded edges on our embedded pages.

AC:

Make /embed/leaderboard have the same rounded edge as /embed/potd

Note: If you need to test this, you can use staging and any HTML page (you can create one on codepen.io
You need to apply the following styles to the codepen.io page to make the embed responsive
```
iframe, object, embed {
    max-width: 100%;
    width: 100%;
}
```

You can then use this iframe element inside the HTML

<iframe
  width="600"
  height="400"
  src="<https://stg.codebloom.patinanetwork.org/embed/leaderboard?patina=true&pageSize=5>"
  title="Codebloom"
  frameborder="0"
  allow="clipboard-write;"
  referrerpolicy="strict-origin-when-cross-origin"
  allowfullscreen=""
  spellcheck="false">
</iframe>