qmenubar hides when resoultion of the monitor changes

[wagmare]

hi friends,
i am facing a strange problem with qmenubar. i am developing the mainwindow with a resolution of 13608768 . i created a menubar and altered with some stylesheet

QMenuBar { padding-left:-4px; spacing: 8px; background-color: qlineargradient(s); 
               border-bottom-width: 1px; 
            border-bottom-color: rgb(26,131,212);} 
 QMenuBar::item {
            padding: 1px 4px;background: transparent; border-radius: 0px;
}
  QMenuBar::item:selected { 
          background: z); 
    color:rgb(255,255,255);} 
QAction {spacing: 3px;}"

QMenuBar { padding-left:-4px; spacing: 8px; background-color: qlineargradient(s); 
               border-bottom-width: 1px; 
            border-bottom-color: rgb(26,131,212);} 
 QMenuBar::item {
            padding: 1px 4px;background: transparent; border-radius: 0px;
}
  QMenuBar::item:selected { 
          background: z); 
    color:rgb(255,255,255);} 
QAction {spacing: 3px;}"

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and from my screen resolution the qmenubar is coming perfect as normal.jpg
but when i tested the ui with bigger monitor
the qmenubar is coming like all the menuitem are formed as a drop down list at the right corner of the menubar
like this ExtentMenuBar.png

please hep me in solving the problem .