Custom TableWidget QHeaderView

[IknowQT]

class QCustomTableView : public QTableWidget
{
	Q_OBJECT

private:
	QHeaderView*	m_pHeaderview;

public:
	QCustomTableView(QObject* parent);
	QCustomTableView(Qt::Orientation orientation, QObject *parent);
}

QCustomTableView::QCustomTableView(Qt::Orientation orientation, QObject *parent)
{
	m_pHeaderview = new QHeaderView(orientation, this);
	this->setHorizontalHeader(m_pHeaderview);
        this->setEditTriggers(QAbstractItemView::EditTrigger::NoEditTriggers);		
	this->horizontalHeader()->setStretchLastSection(true);

QString strStyle("\
				QHeaderView::section\
				{\
					background-color: #00599C;\
					padding: 4px;\
					border: 40px;\
					border-color: red;\
					font-family: Microsoft YaHei UI;\
					font-size: 10pt;\
					color: #FFFFFF;\
				}\
				QTableWidget\
				{\
					gridline-color: #003863;\
					font-size: 10pt;\
					border: 4px;\
					border-color: #002039;\
				}\
				QTableWidget QTableCornerButton::section\
				{\
					background-color: #00599C;\
					border: 4px solid #003863;\
				}\
		");

	this->setStyleSheet(strStyle);
}

I made a customized table widget, but the horizontal header is not accessible and null, so I made a new one and put it in the set horizontal header.
But the style sheet didn't work. I used to check the style sheet.

Is there a way?

[JoeCFD]

my m_tableWidget->horizontalHeader() is not null. Why is yours null? Which Qt version? Mine is Qt 5.15.2.