Add Box component

[felixhabib]

This change:

• Moves vars into its own file (from sprinkles.css.ts)
• Adds a Box component, getting props from sprinkles
• Adds auto as a margin space option in sprinkles
• Uses Box in place of flexGrow and margin: auto for layout where appropriate
• Removes unused classes in Toolbar.css.ts

Continuing the work from #357 and #355 so will share the same changeset

[changeset-bot]

⚠️ No Changeset found

Latest commit: 26418e5

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR