如何在PySide2 of PyQt5中删除QComboBox向下箭头的边框？

from PySide2.QtWidgets import QApplication, QComboBox, QProxyStyle, QStylePainter, QStyleOptionComboBox

class CustomStyle(QProxyStyle):
    def drawComplexControl(self, control, option, painter, widget=None):
        if control == QStyle.CC_ComboBox and option.subControls == QStyle.SC_ComboBoxArrow:
            return
        super().drawComplexControl(control, option, painter, widget)

app = QApplication([])
app.setStyle(CustomStyle())

combo = QComboBox()
combo.addItems(["Option 1", "Option 2", "Option 3"])
combo.show()

app.exec_()