How to provide a CSS class name to the popup of a QSelect or similar?

[davthedev]

Some components trigger popups that are attached to the DOM close to the root, outside the scope of the parent component. Therefore, they are difficult to customize using CSS classes.

The solution would be to pass a CSS class name to use and apply to the root of the popup. Not all seem to provide a way to do so. I would like to style specific instances in a specific part of my application, therefore a generic CSS rule that target the internal classes of the component would not be a solution in this case. Is there an alternative?

Affected components so far I found out: QPopupMenu, QMenu (have to confirm), QSelect (the dropdown popup), QColorPicker.