[TrevorBurnham]

Description

Icon hover-motion CSS, emitted when the One theme is included, is ~300 KB raw per copy of the library. Most of that is selector text: every hover rule repeats a long prefix (theme gate, trigger, disabled guard, target) once per trigger state, and there are four states since #5161.

This PR makes two output-only changes to src/icon/hover-motion.scss:

1. All trigger states share one selector: :is([data-awsui-motion-trigger~=hover]:is(:hover, :focus-visible), [data-awsui-motion-trigger~=focus]:focus-visible, [data-awsui-motion-trigger~=delegated-focus]:focus-within:where(...)):not(:disabled):not([aria-disabled=true]). Each arm has the same specificity as the separate selectors it replaces, so the cascade is unchanged. No :has() is reintroduced.
2. Specs that emit the same declarations on the same part share a rule via .icon:is(.name-a, .name-b). An icon has a single name class, so merging across icons cannot change the cascade.

lib/components/icon/styles.scoped.css with INCLUDE_ONE_THEME=true:

	main	this PR
Raw	312.6 KB	136.9 KB
Minified	298.4 KB	125.9 KB
Minified + gzip	9.7 KB	7.2 KB
Minified + brotli	7.7 KB	5.5 KB

Builds without the One theme are unaffected (no motion CSS is emitted).

Related links, issue #, if available: n/a

How has this been tested?

• New unit tests check that icons with identical motion share a rule and that no two rules differ only in the icon name. Existing selector-shape tests were updated for the merged selector.
• Compared a One-theme build of this branch against main: every other CSS file under lib/components is byte-identical.
• Expanding the merged selectors back into separate ones yields the same 1,008 selectors with the same declarations as main.
• Compared computed styles in Chrome for all 80 animated icons, old CSS vs new, across hover, focus and delegated-focus triggers, disabled and motion-off controls, and both prefers-reduced-motion settings. All 693,120 property comparisons matched.

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 93.88%. Comparing base (fdb6ffa) to head (3df62ae).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5156      +/-   ##
==========================================
- Coverage   97.72%   93.88%   -3.85%     
==========================================
  Files         995      994       -1     
  Lines       32129    27830    -4299     
  Branches    11851     9576    -2275     
==========================================
- Hits        31399    26127    -5272     
- Misses        684      784     +100     
- Partials       46      919     +873     

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