RetroShare/retroshare-gui/src/qss/groove.qss

.QWidget{

   	background-color: qlineargradient(x1: 0, y1: 0, x2: 0, y2: 1,stop: 0 #6799B3, stop: 1 #377a90);
}


/* Customize the toolbar. */
QToolBar {
   	background-color: qlineargradient(x1: 0, y1: 0, x2: 0, y2: 1,
								   stop: 0 #6799B3, stop: 0.3 #377a90, 
								   stop: 0.31 #0e5e73, stop: 1 #4b8598);

    border: 1px solid #4b8598;
}

QTreeWidget::item:selected { /* when user selects item using mouse or keyboard */
   	background-color: qlineargradient(x1: 0, y1: 0, x2: 0, y2: 1,
								   stop: 0 #6799B3, stop: 0.3 #377a90, 
								   stop: 0.31 #0e5e73, stop: 1 #4b8598);

}