chore: Change theme global selector from :root to body

[jkuelz]

Description

Changed CSS theme selectors from :root to body in style-dictionary files across all theme config modules to ensure proper theme application once seed and reference token generation is added to theming-core.

We won't be resolving reference tokens to their hex value until the end of the resolution chain to allow for theming at a global level without having to replace every token value (300+ tokens). Because we are keeping the references as css values, :root has a higher specificity that doesn't allow the resolution to complete when there are multiple themes applied (primary, secondary). Using body as a global selector fixes the specificity issues.

Pre-req: theming-core PR to be in live.

Related links, issue #, if available: [ac9YAbqsd7e6], [CR-229505364]

How has this been tested?

Dev pipeline: Awsui-v3-jkuelz

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.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

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 97.16%. Comparing base (4806683) to head (778d59e).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3957   +/-   ##
=======================================
  Coverage   97.16%   97.16%           
=======================================
  Files         854      854           
  Lines       24981    24981           
  Branches     8802     8801    -1     
=======================================
  Hits        24274    24274           
- Misses        659      701   +42     
+ Partials       48        6   -42     

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