The flag requests that the window's title bar is drawn without a
background color. This flag is useful in combination with the
Qt::ExpandedClientAreaHint flag, to give the perception that the
window's client area seamlessly blends with the titlebar area
and controls.
Task-number: QTBUG-127634
Change-Id: I1194630d737ae03324f79d2babd7ea3d8fca3d5b
Reviewed-by: Assam Boudjelthia <assam.boudjelthia@qt.io>
a1e6fed449