How can I change the white color in QComboBox?

I would like to change the color or adjust the size of this rectangle behind the open Combobox

I noticed that there is a problem with the increased size of this white background and the offset options compared to when this qss is not used Closed ComboBox

Open ComboBox

Here is a code example that recreates this problem:

import sys
from PyQt5.QtWidgets import QApplication, QMainWindow, QComboBox, QVBoxLayout, QWidget


class MainWindow(QMainWindow):
    def __init__(self):
        super().__init__()
        self.setWindowTitle("QComboBox Demo")
        self.setGeometry(100, 100, 300, 200)

        central_widget = QWidget()
        self.setCentralWidget(central_widget)
        layout = QVBoxLayout(central_widget)

        formats = [
            "BMP", "Iris", "PNG", "JPEG", "JPEG 2000", "Targa", "Targa Raw"
        ]

        combo_box = QComboBox()
        combo_box.addItems(formats)
        combo_box.setCurrentIndex(-1)

        layout.addWidget(combo_box)
        layout.addStretch()

        style_sheet = """
        QWidget {
            background-color: #404040;
            color: #e6e6e6;
            margin: 0px;
        }
        QComboBox {
            background-color: #2c2c2c;
            border: 1px solid #404040;
            color: #d0d0d0;
            padding: 4px 6px;
            border-radius: 4px;
            margin: 0px;
        }
        QComboBox:disabled {
            background-color: #323232;
            color: #8a8a8a;
        }
        QComboBox::down-arrow {
            background-color: #2c2c2c;
            image: url('images/QComboBox_down_arrow.png');
        }
        QComboBox::down-arrow:on {
            background-color: #5680c2;
        }
        QComboBox::drop-down {
            background-color: #202020;
            border: none;
            width: 20px;
        }
        QComboBox:on {
            background-color: #5680c2;
            color: #f8f9f9;
        }
        QComboBox QAbstractItemView {
            background-color: #232323;
            border: 1px solid #404040;
            color: #d0d0d0;
            border-radius: 4px;
            margin: 0px;
            padding: 2px;
            min-width: 100px;
            selection-background-color: #5680c2;
        }
        """
        self.setStyleSheet(style_sheet)


if __name__ == "__main__":
    app = QApplication(sys.argv + ['-platform', 'windows:darkmode=1'])
    app.setStyle('Fusion')
    window = MainWindow()
    window.show()
    sys.exit(app.exec_())

Also this partly corrected when I don't use Fusion style, but also some of the necessary style is lost.

The style is based on hannes delbeke stylesheet: https://github.com/hannesdelbeke/blender-qt-stylesheet/blob/main/blender_stylesheet/blender_stylesheet.qss

I got an acceptable working version, using QApplication.setStyleSheet() in the main (I don't know why it works exactly like that...).

New code:

import sys
from PyQt5.QtWidgets import QApplication, QMainWindow, QComboBox, QVBoxLayout, QWidget


class MainWindow(QMainWindow):
    def __init__(self):
        super().__init__()
        self.setWindowTitle("QComboBox Demo")
        self.setGeometry(100, 100, 300, 200)

        central_widget = QWidget()
        self.setCentralWidget(central_widget)
        layout = QVBoxLayout(central_widget)

        formats = [
            "BMP", "Iris", "PNG", "JPEG", "JPEG 2000", "Targa", "Targa Raw"
        ]

        combo_box = QComboBox()
        combo_box.addItems(formats)
        combo_box.setCurrentIndex(-1)

        layout.addWidget(combo_box)
        layout.addStretch()


if __name__ == "__main__":
    style_sheet = """
                    QWidget {
                        background-color: #404040;
                        color: #e6e6e6;
                        margin: 0px;
                    }
                    QComboBox {
                        background-color: #2c2c2c;
                        border: 1px solid #404040;
                        color: #d0d0d0;
                        padding: 4px 6px;
                        border-radius: 4px;
                        margin: 0px;
                    }
                    QComboBox:disabled {
                        background-color: #323232;
                        color: #8a8a8a;
                    }
                    QComboBox::down-arrow {
                        background-color: #2c2c2c;
                        image: url('images/QComboBox_down_arrow.png');
                    }
                    QComboBox::down-arrow:on {
                        background-color: #5680c2;
                    }
                    QComboBox::drop-down {
                        background-color: #202020;
                        border: none;
                        width: 20px;
                    }
                    QComboBox:on {
                        background-color: #5680c2;
                        color: #f8f9f9;
                    }
                    QComboBox QAbstractItemView {
                        background-color: #232323;
                        border: 1px solid #404040;
                        color: #d0d0d0;
                        border-radius: 4px;
                        margin: 0px;
                        padding: 2px;
                        min-width: 100px;
                        selection-background-color: #5680c2;
                    }
                    """

    app = QApplication(sys.argv + ['-platform', 'windows:darkmode=1'])

    app.setStyleSheet(style_sheet)

    app.setStyle('Fusion')

    window = MainWindow()
    window.show()
    sys.exit(app.exec_())