Qwt legend can't fully displayed when dock to right

[SupperPotato]

Describe Your Environment

• QDarkStyle:3.0.2
• OS:Windows 10

Language

C++

Description / Steps to Reproduce [if necessary]

[Description of the issue]
I applyed the qdarkstyle in my project which contians qwtplots,when I set Qwt legend dock to right, legend can't fully display.

    auto m_legend = new QwtLegend(ui->qwtPlot->canvas());
    ui->qwtPlot->insertLegend(m_legend,QwtPlot::RightLegend);
    m_legend->setMinimumWidth(90);
    m_legend->setDefaultItemMode(QwtLegendData::Checkable);
    auto curve=new QwtPlotCurve("testcureve01");
    curve->attach(ui->qwtPlot);

Actual Result

Here is the image actually:

Expected Results / Proposed Result

Here is the image expected ,the legend fully displayed.