How to style the system buttons of a MdiWindow

Hello,

I am trying to create a dark background style for an application. When using the style below the the system buttons(minimize / maximize / close of the mdi window are not styled. Has anyone an idea how to style those buttons?

Regards,

Marcel

Code:

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QAbstractScrollArea {
    background-color: lightgray;
}
 
QCheckBox {
    background-color: lightgray;
}
 
QComboBox {
    background-color: lightgray;
}
 
QComboBox QAbstractItemView {
    color: black;
    background-color: lightgray;
}
 
QDateEdit {
    background-color: lightgray;
}
 
QDateTimeEdit {
    background-color: lightgray;
}
 
QDockWidget {
    color: rgb(220,221,226);
    background-color: rgb(86,96,123);
}
 
QFileDialog {
    color: rgb(220,221,226);
    background-color: rgb(86,96,123);
}
 
QFrame {
    color: rgb(220,221,226);
    background-color: rgb(86,96,123);
}
 
QGroupBox {
    color: rgb(220,221,226);
    background-color: rgb(86,96,123);
}
 
QHeaderView {
    color: rgb(220,221,226);
    background-color: rgb(86,96,123);
}
 
QLineEdit {
    background-color: lightgray;
}
 
QListView {
    color: rgb(220,221,226);
    background-color: rgb(86,96,123);
}
 
QMainWindow {
    color: rgb(220,221,226);
    background-color: rgb(86,96,123);
}
 
QMainWindow > QWidget {
    color: rgb(220,221,226);
    background-color: rgb(86,96,123);
}
 
QMainWindow QDialog {
    color: rgb(220,221,226);
    background-color: rgb(86,96,123);
}
 
QMainWindow QMessageBox {
    color: rgb(220,221,226);
    background-color: rgb(86,96,123);
}
 
QMainWindow QStatusBar {
    color: rgb(220,221,226);
    background-color: rgb(86,96,123);
}
 
QMenu {
    color: rgb(220,221,226);
    background-color: rgb(86,96,123);
}
 
QMenuBar {
    color: rgb(220,221,226);
    background-color: rgb(86,96,123);
}
 
QProgressBar {
    color: rgb(220,221,226);
    background-color: rgb(86,96,123);
    border: 2px solid grey;
    border-radius: 4px;
    text-align: center;
}
 
QProgressBar::chunk {
    background-color: silver;
}
 
QPushButton {
    color: rgb(220,221,226);
    background-color: rgb(86,96,123);
	border-color: navy; /* make the default button prominent */
}
 
QRadioButton {
    color: rgb(220,221,226);
    background-color: rgb(86,96,123);
}
 
QScrollBar {
    color: rgb(220,221,226);
    background-color: rgb(86,96,123);
}
 
QSizeGrip {
    color: rgb(220,221,226);
    background-color: rgb(86,96,123);
}
 
QSlider {
    color: rgb(220,221,226);
    background-color: rgb(86,96,123);
}
 
QSpinBox {
    color: lightgray;
    background-color: lightgray;
}
 
QSplitter {
    color: rgb(220,221,226);
    background-color: rgb(86,96,123);
}
 
QStatusBar {
    color: rgb(220,221,226);
    background-color: rgb(86,96,123);
}
 
QTabWidget {
    color: rgb(220,221,226);
    background-color: rgb(86,96,123);
}
 
QTabBar {
    background-color: rgb(86,96,123);
}
 
QTabBar::tab {
 color: rgb(220,221,226);
 background: rgb(86,96,123);
 border: 1px solid #C4C4C3;
 border-bottom-color: #C2C7CB; /* same as the pane color */
 border-top-left-radius: 3px;
 border-top-right-radius: 3px;
 min-width: 8ex;
 padding: 2px;
}
 
QTabBar::tab:selected, QTabBar::tab:hover {
 background: rgb(12,96,123);
}
 
QTabBar::tab:selected {
 border-color: #9B9B9B;
 border-bottom-color: #C2C7CB; /* same as pane color */
}
 
QTabBar::tab:!selected {
 margin-top: 2px; /* make non-selected tabs look smaller */
}
 
QTableView {
    color: rgb(220,221,226);
    background-color: rgb(86,96,123);
}
 
QToolBar {
    color: rgb(220,221,226);
    background-color: rgb(86,96,123);
}
 
QToolBox {
    background-color: lightgray;
}
 
QToolButton {
    color: rgb(220,221,226);
    background-color: rgb(86,96,123);
}
 
QToolTip {
    color: rgb(220,221,226);
    background-color: rgb(86,96,123);
}
 
QTreeView {
    color: rgb(220,221,226);
    background-color: rgb(86,96,123);
}

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