Visual engine needs to handle white text in dark mode

[TazeYoung]

Issue description: in dark mode, the visual engine does not handle white text well.
In MS Word in dark mode, the solution converts the text into HTML as white text. With the white background of the dialogue box, it makes it very difficult to read.

Similarly, in Chrome, colour contrasts (for example the syllabification shading) are not adequate when the text is white (or off-white) when using dark mode.