如何更改Qt滑块的边框？

// 创建一个QSlider对象
QSlider *slider = new QSlider(Qt::Horizontal);

// 设置滑块的样式表
slider->setStyleSheet("QSlider::groove:horizontal {"
                      "border: 1px solid #999999;"
                      "height: 8px;"
                      "background: qlineargradient(x1:0, y1:0, x2:0, y2:1, stop:0 #B1B1B1, stop:1 #c4c4c4);"
                      "margin: 2px 0;"
                      "}"

                      "QSlider::handle:horizontal {"
                      "background: qlineargradient(x1:0, y1:0, x2:1, y2:1, stop:0 #b5b5b5, stop:1 #8f8f8f);"
                      "border: 1px solid #5c5c5c;"
                      "width: 18px;"
                      "margin: -2px 0;"
                      "border-radius: 3px;"
                      "}");

// 显示滑块
slider->show();