Corrected top search area css media query param

What does this MR do?

Corrects top search area css media query so it switches styles at the correct screen size.

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

It's a regression so likely

Why was this MR needed?

UX

What are the relevant issue numbers?

Closes #18490 (closed). (This stops the search bar dropping into its own row until it needs to be 100% column stacked anyway)

Screenshots (if relevant)

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 style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together