Python - PyQt - transparent background

from PyQt5 import QtWidgets, QtCore

app = QtWidgets.QApplication([]) # or sys.argv

win = QtWidgets.QWidget()

# transparent window but with frame/border
win.setAttribute(QtCore.Qt.WA_TranslucentBackground)

# remove frame/border
win.setWindowFlags(QtCore.Qt.FramelessWindowHint)

button = QtWidgets.QPushButton("HELLO", win)
button.setGeometry(50, 50, 50, 50)
button.clicked.connect(win.close)

# partially transparent button
button.setStyleSheet("QWidget {background-color: rgba(50,50,50,128)}")

#win.setWindowOpacity(0.5)

win.show()

app.exec_()