CSS styling on QPushButton not respected when child is QHBoxLayout

#include<QApplication>
#include<QPushButton>
#include<QLabel>
#include<QVBoxLayout>
#include<QHBoxLayout>
int main(int argc, char **argv)
{
    QApplication app(argc, argv);
    auto window = new QWidget();
    auto layout = new QVBoxLayout(window);

    auto btn1 = new QPushButton("test1");

    auto btn2 = new QPushButton();
    auto labelBtn2 = new QLabel("test2", btn2);

    auto btn3 = new QPushButton();
    auto layoutBtn3 = new QHBoxLayout(btn3);
    auto labelBtn3_1 = new QLabel("test3_1");
    auto labelBtn3_2 = new QLabel("test3_2");
    layoutBtn3->addWidget(labelBtn3_1);
    layoutBtn3->addWidget(labelBtn3_2);

    layout->addWidget(btn1);
    layout->addWidget(btn2);
    layout->addWidget(btn3);

    window->setProperty("class", "window");
    window->setStyleSheet(
        ".window { background:rgba(0,0,0,.5); }"
        "QPushButton, QPushButton QLabel {"
            "color:white;"
        "}"
        "QPushButton {"
            "background-color:rgba(255,0,0,.5);"
            "color:white;"
            "border:0;" //<-- if not present, background is not transparent, but if present, text is no longer shown
        "}"
        );
    window->show();

    return app.exec();
}