In user research we quite often saw people accidentally scroll the
branding preview `<iframe>` when trying to scroll the page.
This is suboptimal because they:
- were confused why the page wasn’t scrolling
- lost visibility of the branding they were trying to preview because
it scrolled outside the bounds of the `<iframe>`
This means we:
- don’t have to copy and paste the `<iframe>` code to every place where
we use it
- can make changes to it in one place and have it apply everywhere
