Thank you DiapDealer. I had been in the Preferences > Appearances and under the Code View tab I'd seen color settings for everything except the background and I hadn't expanded my thinking sufficiently to imagine it was under the OS themes control.
I don't have either kvantum or qt5-ct installed and I am reluctant to explore too far at the moment because UbuntuStudio 22.04.1 LTS should be released in the next 2 or 3 weeks and that will involve a change from XFCE to KDE Plasma so no doubt there will be subsequent changes to get to live with as well. That will remain for a longer-term solution, possibly.
But thanks to your hints, I found a high contrast appearance > style setting in the OS system settings that does the job for the Code View window in Sigil. It also does revolting things to the icon bar but I can live with that for the duration of a few screenshots.
|