Tried your example and it works on Qt5
Widget::Widget(QWidget *parent) :
QWidget(parent),
ui(new Ui::Widget)
{
ui->setupUi(this);
this->setStyleSheet(
"QPushButton#evilButton {"
"background-color: red;"
"border-style: outset;"
"border-width: 2px;"
"border-radius: 10px;"
"border-color: beige;"
"font: bold 14px;"
"min-width: 10em;"
"padding: 6px; }"
);
}
btw I store qss in file and load styles from it