QMenu stylesheet and alpha coloring

[StaticPhilly]

hello all,

I have a QMenu, now in my stylesheet iv tryed:

QMenu
{
	background: rgba(0, 0, 0, 120);
}

QMenu
{
	background: rgba(0, 0, 0, 120);
}

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Now i was hoping it would give a semi-transparent background on the drop down menu, so you could half see the applications qwidget below it.

However what the above does is makes the background without alpha, basiclly its just blank rather then a semi-transparent black.

can oneone point me in the right direction on achiving this or tell me were im going wrong.

thanks,
Phil