In macOS dark mode QWebEngineView's scrollbars are drawn with a light theme

The scrollbars in QWebEngineView draw in the wrong style if dark mode is enabled, other controls that use scrollbars draw correctly, but not QWebEngineView.

There appears to be no way of fixing this without modifying the Qt source.

A screen capture showing this effect is attached.

Simple example is just to add a QWebEngineView and set the URL to a page that has scrollbars.