Austenem/CAT-955 Fix header bug

[austenem]

Summary

Fixes a bug resulting from #3569 that caused the entity header to cut off the top of the page. This was addressed by taking a different approach to fixing the entity header bug that was resolved in #3569, which resolved both issues.

Original bug: header shifted off-screen on initial page load on narrow browser window sizes.
New bug: header cut off the top of the page (due to being removed from the document flow).

Design Documentation/Original Tickets

CAT-955 Jira ticket

Testing

Tested that both bugs were resolved in Chrome and Safari.

Screenshots/Video

Original bug on prod:

trimmed-prod.mov

Resolved original bug locally:

Screen.Recording.2024-10-16.at.9.57.50.AM.mov

Resolved new bug locally:

Screen.Recording.2024-10-16.at.10.23.16.AM.mov

Checklist

• Code follows the project's coding standards
  • Lint checks pass locally
  • New CHANGELOG-your-feature-name-here.md is present in the root directory, describing the change(s) in full sentences.
• Unit tests covering the new feature have been added
• All existing tests pass
• Any relevant documentation in JIRA/Confluence has been updated to reflect the new feature
• Any new functionalities have appropriate analytics functionalities added