Add changes regarding issue #68092

[ronakganatra9]

What?

This PR will add necessary core styles to the BlockCanvas for the storybook project as discussed on #67048
and merged
https://github.com/WordPress/gutenberg/blob/trunk/platform-docs/docs/intro.md

Why?

To fix the story box component

How?

Added necessary styles as mentioned in the documenation

Testing Instructions

Find screenshot below.

Testing Instructions for Keyboard

Screenshots or screencast

Before Screenshot:

After Screenshot:

Before	After

[github-actions]

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[github-actions]

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[stokesman]

Thanks for the PR! I’ve yet to test this but noticed a couple things I think should be changed.