fix(treeview): update Treeview margin and focus border to use Spectrum tokens

[jonnykry]

Description

No specific issue for this change. While working on a Treeview implementation, I noticed two lines of the CSS where we could use Spectrum tokens.

How and where has this been tested?

Tested locally by:

• Adding the changes to my existing Tree View implementation
• Running spectrum-css Storybook locally

Validation steps

Validate visual Tree View before and after, specifically for margin and focus border visual differences. They should be identical.

Regression testing

Validate:

1. The documentation pages for at least two other components are still loading, including:

• The pages render correctly, are accessible, and are responsive.

2. If components have been modified, VRTs have been run on this branch:

• VRTs have been run and looked at.
• Any VRT changes have been accepted (by reviewer and/or PR author), or there are no changes.

Screenshots

To-do list

• I have read the contribution guidelines.
• I have updated relevant storybook stories and templates.
• I have tested these changes in Windows High Contrast mode.
• If my change impacts other components, I have tested to make sure they don't break.
• If my change impacts documentation, I have updated the documentation accordingly.
• ✨ This pull request is ready to merge. ✨

[changeset-bot]

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Latest commit: 71e99e0

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