Stylesheet not fully applied

[GeniusProgger]

A global Stylesheet is not correctly/fully applied/inherited to UI elements inside CTK elements.

For example, a QPushButton inside a ctkCollapsibleGroupBox. The background-color of the pushbutton is not set correctly.

Even setting the following stylesheet directly onto the ctkCollapsibleGroupBox does not work:
setStyleSheet("QPushButton {background-color: red; color: green;}");

The button text becomes green, but the background is not red (it is white).

A quick additional test shows that only QPushButton is incorrect, the following elements inside the groupbox respect the style:
QRadioButton, QCheckBox, QToolButton, QSpinBox, QDoubleSpinBox, QLineEdit