Created attachment 184266 [details]
Screenshot of issue for GNOME dark mode and LO 7.6

Steps:
0. Use the operating system's dark mode
1. Open Writer
2. File > New > HTML document (now using the Writer/Wed editor)
3. Write a couple of words
4. View > HTML source

Results:
Poor choice of colours (e.g. black on dark grey, or bright blue), bad contrast makes it hard to read.
Changing the Application Colours to "LibreOffice Dark" has no effect.

Version: 7.6.0.0.alpha0+ (X86_64) / LibreOffice Community
Build ID: ad387d5b984c6666906505d25685065f710ed55d
CPU threads: 8; OS: Linux 5.15; UI render: default; VCL: gtk3
Locale: en-AU (en_AU.UTF-8); UI: en-US
Calc: threaded

and

Version: 6.3.6.2
Build ID: 2196df99b074d8a661f4036fca8fa0cbfa33a497
CPU threads: 8; OS: Linux 5.15; UI render: default; VCL: gtk3; 
Locale: en-AU (en_AU.UTF-8); UI-Language: en-US
Calc: threaded

Same on Windows:

Version: 7.6.0.0.alpha0+ (X86_64) / LibreOffice Community
Build ID: 9b46020c262045aed0beace4708565235c2523cc
CPU threads: 4; OS: Windows 10.0 Build 19045; UI render: Skia/Raster; VCL: win
Locale: en-GB (en_GB); UI: en-GB
Calc: threaded

LO 6.2 used to use red instead of black, which in my opinion was a little easier to read but obviously a bad choice.

Aware of the argument to entirely remove Writer/Web in bug 95861 but in absence of moving forward with it, this is an accessibility issue.