Fix SubNav underline

[joshfarrant]

Summary

List of notable changes:

What should reviewers focus on?

Steps to test:

Supporting resources (related issues, external links, etc):

• Closes 🐛 [BUG] - Visual issue with SubNav underline #789

Contributor checklist:

• All new and existing CI checks pass
• Tests prove that the feature works and covers both happy and unhappy paths
• Any drop in coverage, breaking changes or regressions have been documented above
• New visual snapshots have been generated / updated for any UI changes
• All developer debugging and non-functional logging has been removed
• Related issues have been referenced in the PR description

Reviewer checklist:

• Check that pull request and proposed changes adhere to our contribution guidelines and code of conduct
• Check that tests prove the feature works and covers both happy and unhappy paths
• Check that there aren't other open Pull Requests for the same update/change

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Latest commit: f93e7f4

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⚠️ Visual differences found

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