请教怎样改变QGroupBox的边框线的粗细啊

请问怎样改变QGroupBox的边框线的粗细啊？
如题？

[解决办法]
QSS
[解决办法]
setStyleSheet(
"QGroupBox"
"{"
" border: 3px solid;"
"}"
);
[解决办法]

C/C++ code

QGroupBox *leftButtonGroup=new QGroupBox; leftButtonGroup->setStyleSheet(QObject::tr(" border: 3px solid;"));