Routing Boot Package: Remove margin and border-radius from layout components

[SirLouen]

What?

Continues #75036

Why?

@youknowriad commented that when adding Styles in profile, the background was popping for the new layout components

How?

Instead of removing the background, which may make sense in the future with a future admin redesign, simply fully expanding the margins to cover the whole scene and removing the rounded corners fixes the thing while maintaining all backgrounds.

Testing Instructions

1. Go to Users > Profile
2. Switch your Administration Color Scheme to "Blue" for example
3. Go to Appearance > Fonts
4. You will see those black margins right and bottom

Screenshots or screencast

Before	After

[github-actions]

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[youknowriad]

this only solves the issue partially for me. I think the "extensible site editor"'s sidebar color should also adapt to the profile. and I'm on the fence about removing the padding on the fonts screen, it's good that it's closer to site editor design, kind of bridges both.

[SirLouen]

this only solves the issue partially for me. I think the "extensible site editor"'s sidebar color should also adapt to the profile. and I'm on the fence about removing the padding on the fonts screen, it's good that it's closer to site editor design, kind of bridges both.

You mean something like this?

[youknowriad]

Yes :)

[SirLouen]

Yes :)

I think we are going to need to work on a Core patch to expose these colors cleanly for Gutenberg. Let me check the thing, and I will ping you there to see if we can make it.

[SirLouen]

Added upstream: #64571

[SirLouen]

I've also switched to #1d2327 as this is the default base color for the Default color scheme. But I can revert back to the #f0f0f0 fallback