Python setStyleSheet()，父窗口QWidget设置背景图不生效问题

import sys
from PyQt5.QtWidgets import QWidget, QApplication, QVBoxLayout, QPushButton, QComboBox, QStyleOption, QStyle
from PyQt5.QtCore import Qt
from PyQt5.QtGui import QKeyEvent, QIcon, QPixmap, QPaintEvent, QPainter

class QSSSelector(QWidget):
	def __init__(self):
		super(QSSSelector, self).__init__()

		self.setWindowTitle("窗口最大化和最小化")
		self.resize(500, 500)

		self.setProperty("name", "widget")

		self.button1 = QPushButton("按钮1")
		self.button2 = QPushButton("按钮2")
		self.button2.setProperty("name", "btn2")  # 设置的属性是以键值对方式
		self.button3 = QPushButton("按钮3")
		self.button3.setProperty("name", "btn3")

		self.comboBox = QComboBox()
		self.comboBox.setObjectName("cb")  # 设置对象名字
		self.comboBox.addItems(["windows", "macOS", "linux"])

		self.vLayout = QVBoxLayout(self)
		self.vLayout.addWidget(self.button1)
		self.vLayout.addWidget(self.button2)
		self.vLayout.addWidget(self.button3)
		self.vLayout.addWidget(self.comboBox)

		# 打开qss文件
		with open(r"style sheet.qss", "r", encoding="utf-8") as file:
			qss = file.read()
			print(qss)

		# # 选择器，将所有的PushButton背景改为红色
		self.setStyleSheet(qss)

	def paintEvent(self, a0: QPaintEvent) -> None:  # 设置父窗口背景图时，需要重写paintEvent方法。如果是QMainWidow时不需要。
		opt = QStyleOption()
		opt.initFrom(self)
		painter = QPainter(self)
		# painter.setRenderHint(QtGui.QPainter.Antialiasing) # 反锯齿
		self.style().drawPrimitive(QStyle.PE_Widget, opt, painter, self)


if __name__ == "__main__":
	app = QApplication(sys.argv)
	window = QSSSelector()
	window.show()
	sys.exit(app.exec_())

.QSS文件内容：

QPushButton{
		background-color: red;
	}

QPushButton[name="btn2"]{
		background-color: rgb(100, 50, 50,50);
		color: blue;
		height: 60;
		font-size: 30px;
	}

QComboBox#cb::drop-down {
		image: url(./images/2.png);
	}

QWidget[name="widget"]{
    background-image: url(images/blue.png);
}