Use spectrum css typography and tokens

[jonsnyder]

Description

Updates the extension UI to use Spectrum styles and colors. This has changed the following:

• Headings and titles are now the correct size
• Background color is now gray
• Wells now have a border
• The colors of the tree view have been updated

Related Issue

Motivation and Context

Updating dependencies changed the heading sizes.

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Improvement (non-breaking change which does not add functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have signed the Adobe Open Source CLA or I'm an Adobe employee.
• I have made any necessary test changes and all tests pass.
• I have run the Sandbox successfully.
• I've updated the schema in extension.json or no changes are necessary.
• My change requires a change to the documentation.

[jfkhoury]

Look at that beautiful gray 😆 Thank you Jon!