Fix styles wtih BOM ignored by browsers, leading to UI behavior change

[myovchev]

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Summary

Fixed incorrect sizing and spacing across the admin UI in webpack builds. A byte order mark preserved by PostCSS 8.5.24 invalidated the stylesheet rule setting box-sizing for .apos- elements. Sass is now compiled with charset: false in webpack builds, so the marker is never emitted. Vite builds were unaffected.

What are the specific steps to test this change?

No UI visual change in projects with Webpack builds.

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• Bug fix
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• It includes a) the existing issue ID being resolved, b) a convincing reason for adding this feature, or c) a clear description of the bug it resolves
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If adding a new feature without an already open issue, it's best to open a feature request issue first and wait for approval before working on it.

Other information:

[boutell]

Merged so the next tests of other things pass. Thanks.