UI: Polish canvas and sidebar for 7.0

[MichaelArestad]

What I did

I removed the margins around the preview giving folks back some pixels. This required decoupling the theme's page margin from the draggers, which had some wild side effects before.

How to test

• Is this testable with Jest or Chromatic screenshots?
• Does this need a new example in the kitchen sink apps?
• Does this need an update to the documentation?

[MichaelArestad]

@tmeasday Do you have any ideas on how to get the theme color to show here? If not, I can pull this line of code.

[tmeasday]

Hmmm, not sure, I think @ndelangen knows the most about themes

[ndelangen]

No way to do it there, as the theme is determined at runtime.
And in fact can change at runtime.

At least that's how it is at this point, and will likely stay in 7.0 because changing that will be a breaking change.

Currently users define their theme in manager.ts but in order to know it at build time, it'd have to be moved to main.ts or some preset value.

[domyen]

Thanks for the heads up Norbert! @MichaelArestad let's punt on this meta tag

[MichaelArestad]

Rebased with the new icons.

[shilman]

LGTM, thanks @yannbf for the story fixes!