Advanced Settings collapsible button overlaps with panel title

The Advanced Settings title and button overlap in the editor:

Adding a top margin to `.crx-collapsible > button` resolves the issue (but I don't know if that's the kind of fix you'd prefer).

I'm seeing this in Wagtail 7.1.1 with CRX 6. Changes to [collapsible block settings](https://guide.wagtail.org/en-7.1.x/releases/new-in-wagtail-7-1/#collapsible-blocks-settings) were part of the upgrades for Wagtail 7.1, so maybe that's related.

Reproduce the overlap in the editor using Wagtail 7.1.1 with CRX 6, then inspect the styling for `.crx-collapsible > button` and its surrounding title. Verify the finished change keeps the Advanced Settings title and button separated without disrupting the collapsible control.

Scritto dal modello di indicizzazione a partire dal testo della issue.