SetProperty not working

[kchandr7]

Using Qt Designer, I changed the sytlesheet of my Parent object to

@*[mandatoryField="true"]
{
background-color: rgb(255, 255, 127);
}@

and this works fine. However, when I change this attribute to a font, the effect is not seen on my application.

@*[mandatoryField="true"]
{
font: 28pt "Bitstream Charter";
}@

In my widget code, I am writing this:
@
ui->stackedWidget->setProperty("mandatoryField", true);
ui->label1->setProperty("mandatoryField",true);@

Is there something obvious that I am missing here? How is it that background color applies and not the font?