Currently, the 'Focused Visual Style' for the ListBox item can't be created, edited, or otherwise accessed in Studio.

Repro Steps:

1) Create a Project with a MainPage.xaml
2) Introduce a ListBox Element to the Page
3) Right-Click on the ListBox, navigate to 'Templates', then to the 'ListBoxItemContainer' submenu, and finally, select 'Create'.
This will create a Template and open it in the Template Dummy Editor (Magenta Border).

4) Exit the Template by clicking on the Return Scope button in the lower-right corner.
This will now place you within the Style that contains the ListBoxItemContainer Template. This can be seen from the Orange border around the Stage.

5) Navigate to the Style's Properties Panel, and open the Expander under 'Styling' to reveal the 'Focus Visual Style' Resource Selector.

6) On the row for the Focus Visual Style Property Click the (+) icon to create a new Focus Visual Style.
7) Navigate to the Resources Panel.
Observe how the created Style is not present within the Resources.

Expected Results: Styles created from the Properties Panel are created as Resources.

The inability to create a new Focus Visual Style, alongside the inability to edit the Default Style means that it is not possible for a user to change the appearance of the Focus Visual Style.