This is what I did:

QLabel *label = new QLabel("Sync with entities started by user: " + szUser + ". Please wait...");

label->setStyleSheet("color:rgb(255,255,255);"
                     "font-size: 15px;"
                     "border: 1px solid rgb(72,72,72)");

progressDialogSync.setStyleSheet("QProgressDialog {"
                                 "    background-color:rgb(72,72,72);"
                                 "    padding: 20px;"
                                 "    border: 3px solid rgb(50,50,50);"
                                 "    border-radius: 5px;"
                                 "}"
                                 "QProgressBar {"
                                 "    border: 2px solid white;"
                                 "    padding: 1px;"
                                 "}");

progressDialogSync.setCancelButton(nullptr);
progressDialogSync.setLabel(label);
progressDialogSync.setMinimum(0);
progressDialogSync.setMaximum(0);
progressDialogSync.setAutoClose(true);
progressDialogSync.resize(progressDialogSync.width(), 100);
progressDialogSync.setWindowFlags(Qt::FramelessWindowHint);
progressDialogSync.setWindowModality(Qt::ApplicationModal);

QProgressBar *bar = progressDialogSync.findChild<QProgressBar *>();
bar != nullptr ? bar->setTextVisible(false) : void();

while(bSyncInProgress) {
    progressDialogSync.exec();
}

And this is how it looks:

How do I get rid of that empty space so that my progress bar is either centered or takes up the width of the dialog box.