Global styles code quality refactoring

[ajlende]

Follow-up to fix some code quality issues from #6616.

Gutenberg PR: WordPress/gutenberg#62299

Trac ticket: https://core.trac.wordpress.org/ticket/61370

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Props ajlende.

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[oandregal]

Committed in https://core.trac.wordpress.org/changeset/58339

[oandregal]

@ajlende Appreciate the thoroughness of creating a dedicated trac ticket for this! Given this change is a follow-up to the original ticket, for convenience, we can refer to the original ticket in the PR — no need to create a new one.