[Qt 4.6.3 Linux] style sheet focus on QPushButton

[snooker9]

Hi all!

I'm trying to set the style sheet on my QPushButton to design the frame which seems to be the focus: this frame seems to change of widget when I use "Tab" key.
In the following screenshot, you'll see the button "Valider" which is surrounded by a black frame:
Zimage

I would like to edit his look & feel.
I've tried this code:

QPushButton::focus {  
border: 1px solid blue;  
}

QPushButton::focus {  
border: 1px solid blue;  
}

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But it doesn't work...

Someone there a solution?

I thank you in advance!