PROD-1410 #414-Theme-issue Fix PHP: Add Filter to add style to link tag

[kishanjasani]

All Submissions:

• [x] Have you followed the Pull Requests Guidelines?
• [x] Does your code follow the WordPress' Coding Standards?
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Changes proposed in this Pull Request:

Fixes https://github.com/buddyboss/buddyboss-theme/issues/414

How to test the changes in this Pull Request:

1. Go to forum pages
2. Check the sub forum styles are consistent.

Other information:

• [x] Have you added an explanation of what your changes do and why you'd like us to include them?
• [x] Have you written new tests for your changes, as applicable?
• [x] Have you successfully run tests with your changes locally?