Fix positioning of top scroll button

What does this MR do?

Fix positioning of top scroll button

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

Not really

Why was this MR needed?

Since we are now removing the fixed navigation we need to handle properly the position o scroll buttons.

Screenshots

Before

After

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #28253 (closed)