Chart stylesheet & Text field

[IknowQT]

Hi. I'm drawing the chart real-time. I have a question.
The red letter stage1 starts with the 8.5 number on the x-axis. I want to mark it, so if it's drawn in real time, I'll have to go back in the direction of the arrow. Is there a way to do this?

The second question is, is there a way to decorate the chart like this? Will the chart be a style sheet? And my chart is based on the theme provided by qt, but if the background is white, can you change this color or make it transparent?

[IknowQT]

m_pChartViewer->chart()->setBackgroundVisible(false);
//m_pChartViewer->chart()->setBackgroundBrush(QColor(0, 0, 0, 0));

[IknowQT]

void QTemperatureChart::InitializeChart()
{
	//m_pChartViewer = new QChartView(createAreaChart());
	m_pChartViewer = new QChartView(createSplineChart());
	//m_pChartViewer->chart()->setTheme(QChart::ChartTheme::ChartThemeDark);
	m_pChartViewer->chart()->legend()->hide();
	m_pChartViewer->chart()->setAnimationOptions(QtCharts::QChart::SeriesAnimations);
	m_pChartViewer->chart()->setAnimationDuration(500);
	//m_pChartViewer->chart()->setBackgroundRoundness(20);
	//m_pChartViewer->chart()->setBackgroundVisible(false);
	//m_pChartViewer->chart()->backgr;
	m_pChartViewer->chart()->setBackgroundBrush(QBrush(Qt::darkGray));
	//m_pChartViewer->chart()->setBackgroundVisible(false);
	m_pChartViewer->setRenderHint(QPainter::Antialiasing);
	m_pChartViewer->setBackgroundBrush(QBrush(Qt::darkYellow));
	//m_pChartViewer->setStyleSheet("ChartView{background-color: none;}");
	//m_pChartViewer->setBackgroundBrush(QColor(255,255,255,0));


    this->ui.verticalLayout->addWidget(m_pChartViewer);
}

It's not transparent.