QWebEngineView widget changes the color of the application

I create an application, styled using style sheets with transparent colors (the main window itself is not transparent). When I add a QWebEngineView to the layout, all the colors in the application change.

Below I included a test application in python which reproduces the issue. I also tested in C++, but there I don't have such a distilled example (I used the Extension example, added the style setting to the end of the FindDialog constructor, and connected the moreButton to add the web engine).

Pictures:

 - application at start:

• after pressing the button: