New issue by pullmoll on void-packages repository

https://github.com/void-linux/void-packages/issues/29195

Description:
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### System

* xuname:  
  *Void 5.11.2_2 x86_64 AuthenticAMD uptodate rrrdFFFF*
* package:  
  *qt5-doc*: 5.15.2_1
*qtcreator-full*: 4.14.1_1

### Expected behavior

Readable Courier or monospace font in QtCreator's help viewer.

### Actual behavior

The font used to render the HTML (or *.qch) files is not Courier or monospace as e.g. `/usr/share/doc/qt5/qtcore/style/offline-simple.css` define, but is a proportional font spaced with constant width. It is not scaling with the help window using e.g. `Ctrl +` and `Ctrl -`, and is almost unreadable. This is a screenshot: ![qt5-doc-ugly-courier-monospace](https://user-images.githubusercontent.com/10061347/109787426-7ccb0b80-7c0e-11eb-8a7a-f004acc36b58.png)

### Steps to reproduce the behavior

Install e.q. `qtcreator-full` run it and view the context help with `F1`.

I have no clue why the font used to render the help is this ugly.
Is it a qt5-webengine thing?
Is something missing in the template of qt5-doc?
Is something missing in the template of qtcreator?
Or is just my setup and installed fonts?
Viewing the help files from `/usr/share/doc/qt5/*/*.html` gives sane results in a web browser like Firefox.

Before trying to track down the problem I'd like to ask whether I am the only one facing it.