Spyder dark theme overrides background color set in syntax highlighting theme, except behind text

[CAM-Gerlach]

Problem Description

As discussed in #8020 and part of #8068 .

The background color of the Editor pane, as well as the syntax color scheme preview in preferences, does not change as it should with the "Background" color of the syntax highlighting theme, but rather only the background surrounding the actual text characters. This works properly with the light UI theme. The issue reporting dialog editor has the same problem, except that it always uses the light theme so it looks even worse. Examples:

Spyder dark theme:

Zenburn:

Syntax theme preview:

Issue report:

[ccordoba12]

I know how to fix this. I'll do it once PR #8020 is merged.

[CAM-Gerlach]

@ccordoba12 Also an issue in the internal console, which uses the default syntax highlighting scheme like the issue reporter dialog: