[!] IMPORTANT NOTE [!]
AFTER DISCUSSION, DISREGARD THE BELOW: THIS IS ACTUALLY ABOUT INLINE TEMPLATES BEING LABELLED AS "DEFAULT" IN THE CONTEXT MENU RATHER THAN BEING NAMED "INLINE".
However, not deleting this description or ticket as the context and repro steps still apply.

Currently, in the way the ScrollViewer/ScrollBar is set up at a Template Level, to be able to access the inner contents and customise, we force the user to create a new Template for the ScrollViewer, and we also enforce the same system for the ScrollBar. Neither of these 'Defaults' feature an available 'Edit' action.

This is a great system because if any error is made, or a reversion back to a 'default' is desired, all the user must do is select the Element's 'Default' from the Templates List.

However, once inside the ScrollViewer/ScrollBar Template, the Increase/Decrease Repeat Buttons, as well as the Thumb uniquely feature direct access to Editing the Default Templates. As far as I know, this an exception from how all other Templates are handled within Studio.

What this results in, is that if a user makes edits to any of these parts, any changes they make are permanent, without any way to revert back to each of their defaults.

I'll also note that I believe these Templates are all stored inline, but do not appear in the Resources in any form.

Repro Steps:

1) Create a Studio Project featuring a MainPage.xaml
2) Introduce a ScrollViewer to the Page, and create a new ScrollViewer Template from it. (Any save location, and any name can be assigned).
This will open the ScrollViewer in its inline Template Editor.

3) In the Navigator, identify the PART_VerticalScrollBar, and create a Template from it. (Any save location, and any name can be assigned).

4) Within the PART_VerticalScrollBar, identify the 'Thumb' Element (not the 'Thumb' parent tot he Element), right click on it, and from the 'Templates' category of its Context Menu, observe that the '[Thumb Default] is applied.

5) With the Thumb's Context Menu still open under the Templates Category, select 'Edit Current'.
6) Perform any change to the appearance of the 'Thumb' Border Element (eg: changing 'Background' property colour).

7) In the Resources Panel, attempt to find in the Resources Panel where the 'Thumb Default' Template is stored.
8) Using the Breadcrumb Menu, back one level up, landing in the Style. Once again, attempt to find in the Resources Panel where the 'Thumb Default' Template is stored.
9) Using the Breadcrumb Menu, back one level up, landing in the PART_VerticalScrollBar Template. Once again, attempt to find in the Resources Panel where the 'Thumb Default' Template is stored.

Observe how although a Template was edited, and changes were made, the Template itself is nowhere to be found within Studio or the Project.

10) Close Studio, and Re-Open it.

11) Attempt to restore the ScrollBarThumb to its Default appearance from before the change in Step 6) was performed.

Observe how there is no method to revert to Studio's default presentation of the ScrollBar Thumb.

Expected Results: Inline Templates/Styles that can be edited are visible and accessible in the Resources Panel.

Expected Results: We offer functionality where users user may convert any of their own created Resources at any time to the "Default". These should be allowed to be edited or deleted. If they are deleted, the expectation would be that any Elements would then revert to the "System Default" for that Element.

However, users shouldn't be able to permanently destructively alter the "System Defaults", as this results in essentially corrupting an entire Project where from that point on, the user has lost the ability to ever revert to these safe/functional versions.