Different ViewBox's color in create-content-loader tool

[soknifedev]

It would be nice if the viewbox's color were different from the app-canvas background (currently #fff).

Here is a (horrible) example that I made using the browser's inspector:

As you can see, the viewBox bounds are visible, making it easier to create a loader.

And here is a screenshot of the current app-canvas background where the viewBox is not visible:

What do you think?