How to get rid of strange white line under QTabBar while customzing QDockWidget thru stylesheet

[m. selim]

I do have a QDockWidget that includes tabified dockwidgets.
I am customizing the the QMainWindow stylesheet by the following stylesheet:

QWidget { color:white; background: #757575 }

QTabWidget { padding: 0px; border: 0px; background-color: #757575; }
QTabWidget::pane { border: 0px solid #C2C7CB; top: -3px; background: #757575; }
QTabWidget::tab-bar {
subcontrol-position: top left;

subcontrol-origin: margin;
padding: 0px 0px 0px 0px;
border: 0px;
background: transparent;
}

QTabBar { background-color : #757575; }
QTabBar::close-button {
subcontrol-position: right;
}
QTabBar::tab {
color: white;
background: #757575;
border-top-left-radius: 0px;
border-top-right-radius: 0px;
min-width: 8ex;
padding: 10px;
min-width: 100px;
}

QTabBar::tab::selected{ border-bottom: 0px solid #757575; background-color: darkgrey; }