Help: Titles of some sections in the Help view are black also when using the dark theme

**Describe the bug**
Titles are black and can't be seen in the black background.

Affects at least "See also" and "More results" titles in the context-aware help information.

**To Reproduce**
- Activate the _Dark theme_
- Open the _Help_ (`F1`)

**Expected behavior**
The title should be in white (or is it gray?) like the text above it.

**Screenshots**

**Environment:**
1. Select the platform(s) on which the behavior is seen:
- - [ ] All OS
- - [x] Windows
- - [ ] Linux
- - [x] macOS