Styling QtQuick controls in PySide2 application

main.py

"""
A really simple PySide2 application using QtQuick and Material style

(it should work on PySide6 too)


In order to set a global theme for QtQuick you can use options as described below in the __main__.
You can override style properties in single qml files, if you want

To change the Material theme (dark, light, system) or other material properties you can use a
configuration file called qtquickcontrols2.conf

ref: https://doc.qt.io/qt-5/qtquickcontrols2-configuration.html
     https://doc.qt.io/qt-5/qtquickcontrols2-material.html#material-theme-attached-prop

To make it working you need to add it to a resource file and then compile it to a python file that you need 
to include in your main.py

Recap:
1. create a qtquickcontrols2.conf file:
```
[Controls]
Style=Material


[Material]
Theme=Dark
Accent=Teal
Primary=BlueGrey
```

2. create a resources.qrc file containing qtquickcontrols2.conf
```
<RCC>
    <qresource prefix="/">
        <file>qtquickcontrols2.conf</file>
    </qresource>
</RCC>
```

3. compile qrc file to py file using pyside2 utility
```
pyside2-rcc resources.qrc -o rc_main.py
```

4. import rc_main in your python application

5. set the application to use Material theme with one of the following alternative options:

    - setting the style in the [Controls] section of qtquickcontrols2.conf file
    - passing or overriding the --style argument (see code below)
    - using QtQuickStyle module (see code below)
    - using QT_QUICK_CONTROLS_STYLE environment variable

"""

import sys
import os

from PySide2.QtGui import QGuiApplication
from PySide2.QtQml import QQmlApplicationEngine

from PySide2.QtQuickControls2 import QQuickStyle

import rc_main

if __name__ == "__main__":

    # How to set the style for QtQuick :
    
    # Option 1 - passing or forcing --style argument
    #sys.argv += ['--style', 'material']

    # Option 2 - use QtQuickStyle module
    if not os.environ.get("QT_QUICK_CONTROLS_STYLE"):
        QQuickStyle.setStyle("Material")


    app = QGuiApplication(sys.argv)
    engine = QQmlApplicationEngine()
    engine.load(os.path.join(os.path.dirname(__file__), "main.qml"))

    if not engine.rootObjects():
        sys.exit(-1)
        
    sys.exit(app.exec_())