Make it more obvious that param builders are scrollable

It took me a while to figure out that the arguments for my `POST /wp/v2/posts` endpoint were all being displayed correctly:


(you have to scroll inside the Query box, which was not obvious to me.) Maybe we could add a visual cue to make this more clear?

Reproduce the POST /wp/v2/posts view and inspect the Query box where the arguments are displayed. Determine an unobtrusive visual cue that makes the box's scrollability clear, then verify that all arguments remain accessible and the cue is visible in the console.

Written by the indexing model from the issue text.