Fix tabs container styles to make RSS button clickable

What does this MR do?

Restores ability to click RSS feed button on various pages where tabs container was covering it, making user unable to click button.

Are there points in the code the reviewer needs to double check?

As a part of this MR, following pages (which are impacted by styling changes) have been verified in Chrome, Firefox and Safari;

• /dashboard/activity
• /dashboard/milestones
• /admin/jobs
• /admin/projects
• /admin/users
• /dashboard/projects
• /h5bp/html5-boilerplate/merge_requests (project/merge_requests)
• /search

Why was this MR needed?

Screenshots

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [ ] Documentation created/updated
• [ ] API support added
• [ ] Tests added for this feature/bug
• Review
  • [ ] Has been reviewed by UX
  • Has been reviewed by Frontend
  • [ ] Has been reviewed by Backend
  • [ ] Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• [ ] Internationalization required/considered
• [ ] End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Closes #45398 (closed)