Setting QMainwindow separator width does not work on linux

[cerlin]

I use some QDockwidget for my app layout, put them on top/bottom/left/right area of QMainwindow, remove central widget and set style as

QMainwindow::separator {
   width: 0px;
   height: 0px;
}

On windows pc, there is no extra space between each of them.
But while on linux with the same code,there is always a 10px width separator between them.

Any idea for this issue?