chore: Use simplified styles build

[just-boris]

Description

Use the new internal API added in cloudscape-design/theming-core#72

How has this been tested?

• PR build
• Locally

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (448fb6c) to head (fa1524f).

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #29   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           27        27           
  Lines          318       318           
  Branches        30        30           
=========================================
  Hits           318       318           

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