Styles: Adjust coveo styling to match branding

[TasoOneAsia]

Proposed changes

This PR adjusts styling and font-family definitions to ensure font inheritance and color alignment with NGINX branding.

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After:

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING document
• If applicable, I have added tests that prove my fix is effective or that my feature works
• If applicable, I have checked that any relevant tests pass after adding my changes
• I have updated any relevant documentation (README.md and CHANGELOG.md)

[github-actions]

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[github-actions]

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