Text editor should display a partial view with a drop shadow

[JasonWeill]

The bottom of the page of the text editor shows the white document portion going all the way to the bottom. It should render like a "document" - in other words, a white piece of paper on a grey table.

This was found during a bug bash by @ellisonbg .

See also #6781.

[jtpio]

For reference the editor in the Classic Notebook goes almost all the way to the bottom (it has a small margin bottom):

[jesuscastillx]

Currently waiting on guidance for the shadow aspect of this issue, but I got another PR that fixes the white space :)

[jtpio]

Closing as fixed by #6804