PyQt5 Stylesheet For QWidget's Child To Change QWidget - pyqt5

Question

I have a QWidget with a HBoxLayout inside. Inside this HBoxLayout there is a few buttons and a QLineEdit object. Using stylesheets, I would like to make it so that when the QLineEdit is focused, the QWidget gets a blue outline/border.
I have tried:
QSearchWidgetStyleSheet = QWidget {background-color: rgb(27,27,27); border: none; margin: 0px; border-radius: 3px; padding: 0px;}
QLineEdit:focus {border: 3px solid rgb(100,100,100;}
With my QLineEdit stylesheet being:
QLineEditStyleSheet = QLineEdit {color: white; background-color: rgb(255,255,255,0); border: none; height: 32px; border-radius: 3px; margin-left: 3px; margin-right: 3px;}
However, there is no effect on the QWidget when the QLineEdit is focussed. What should I change in order for the QWidget to get the border/outline when the QLineEdit is focused?

Answer 1

QLineEdit:focus applies the style to the QLineEdit, not the QWidget. While child widgets can take up the style sheet of their parent widget, I don't think it works the other way around in general style sheet syntax. Instead you could describe the scenario only considering the QWidget... It should have a border when it is not in focus, and it should not have a border when it is in focus.
import sys
from PyQt5.QtWidgets import *
from PyQt5.QtCore import *
from PyQt5.QtGui import *
class Widget(QWidget):
def __init__(self):
super().__init__()
hbox = QHBoxLayout(self)
hbox.addWidget(QPushButton('Push'))
hbox.addWidget(QLineEdit())
self.setAttribute(Qt.WA_StyledBackground, True)
self.setStyleSheet('''
Widget {
border: 3px solid blue;
}
Widget:focus {
border: none;
}''')
def mousePressEvent(self, event):
if event.button() == Qt.LeftButton:
self.setFocus()
class Template(QWidget):
def __init__(self):
super().__init__()
grid = QGridLayout(self)
grid.addWidget(Widget(), 0, 0)
self.resize(300, 300)
if __name__ == '__main__':
app = QApplication(sys.argv)
gui = Template()
gui.show()
sys.exit(app.exec_())
Of course if you're open to using other methods, like signals and slots, you could achieve more precisely that functionality.