#include <QtWidgets>

using namespace Qt::StringLiterals;

class MyWidget : public QWidget
{
    Q_OBJECT

public:
    MyWidget()
    {
        auto lw = new QListWidget;

        auto lwi = new QListWidgetItem;
        lw->addItem(lwi);
        lw->setItemWidget(lwi, new QLabel(u"test"_s));

        auto l = new QVBoxLayout(this);
        l->addWidget(lw);
    }
};

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    a.setStyle(u"Fusion"_s);

    a.setStyleSheet(u"MyWidget QLabel {color:red;}"_s);

    MyWidget w;
    w.show();

    return a.exec();
}

#include <main.moc>