self.pushButton.setStyleSheet("background-color: red")
setStyleSheet('QPushButton {background-color: #A3C1DA; color: red;}')
QPushButton button1, button2, button3;
button1.setStyleSheet("background-color: red");
button2.setStyleSheet("background-color:#ff0000;");
button3.setStyleSheet("background-color:rgb(255,0,0)");