- Set the preview canvas to `display:block` to remove vertical spacing
caused by the default value, which was making a full-height canvas cause
vertical scrolling, and the vertical scrollbar caused horizontal
scrolling
- Wrap the preview content in a container with `position:relative` and
no other visible content, so that the full-height iframe excludes the
height of the preview frame header, preventing it from going beyond the
height of the page
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