fix(livedemo): add left border

[tay1orjones]

This updates all live demo preview containers to now have a left border to avoid the issue described in carbon-design-system/carbon#10889 (comment)

Changelog

Changed

• add back the left border to the live demo preview container

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🔍 Inspect: https://vercel.com/carbon-design-system/carbondesignsystem/54qUtNXEDH6m7VkaZJ4T1A9pxJxk
✅ Preview: https://carbondesignsystem-git-fork-tay1orj-f6649e-carbon-design-system.vercel.app

[aagonzales]

Its doing a weird tapper at the corner. Can we get those two border ends squarely meet?

[aagonzales]

Also I think we probably need to border to go all the way across the top as well. Otherwise there's a gap there with the Gray 10 theme

[aagonzales]

@tay1orjones so I thought this was a intentional design decision at some point but maybe was just bug. Instead of the line board, these demos used to have this 8px white boarder. I talked to the other designers and seems like this change wasn't intentional. Can we actually just bring that back?

Its on the v10 demos

[tay1orjones]

@aagonzales Ah! That explains a ton 😅 I see now that we updated the border to use the new tokens, so it's no longer a fixed value but changes with the theme. I'll push an update to fix.

[aagonzales]

Nice!