1 QFrame + QGraphicsDropShadowEffect

QFrame *frame = new QFrame(this);
frame->setStyleSheet("QFrame{background-color: rgb(255, 255, 255);border-radius:10px}"); //设置圆角与背景透明
frame->setGeometry(5, 5, this->width() - 5, this->height() - 5);//设置有效范围框
QGraphicsDropShadowEffect *shadow_effect = new QGraphicsDropShadowEffect(this);
shadow_effect->setOffset(0, 0);
shadow_effect->setColor(Qt::black);
shadow_effect->setBlurRadius(10);
frame->setGraphicsEffect(shadow_effect);
//...
this->setAttribute(Qt::WA_TranslucentBackground);//特别注意这句

如果发现没有效果，那可能你设置了底层布局的问题。因为你可能设置了底层布局setContentsMargins的关系，如是，调整这个函数的参数即可

2 paintEvent

def paintEvent(self, event: QPaintEvent):
    painter = QPainter(self)
    path = QPainterPath()
    path.setFillRule(Qt.WindingFill)
    path.addRect(10, 10, self.width()-20, self.height()-20)
    painter.setRenderHint(QPainter.Antialiasing)
    painter.fillPath(path, QBrush(Qt.white))
    color = QColor(0, 0, 0, 50)
    for i in range(10):
        x = 10-i
        path = QPainterPath()
        path.setFillRule(Qt.WindingFill)
        x1, y1, x2, y2 = x, x, self.width()-x*2, self.height()-x*2
        print(x1, y1, x2, y2)
        path.addRect(x1, y1, x2, y2)
        color.setAlpha(150 - (i**0.5)*50)
        painter.setPen(color)
        painter.drawPath(path)