QSS Styling for Widgets within Widgets

What I'm trying to achieve is to have all the widgets of a certain type that are within another widget to be styled differently from the rest of the application. I've done this before but I can't seem to figure it out. For example:

MyCustomWidget has a layout and many widgets within that layout, including but not limited to QCheckBoxes. I want to style all the QCheckBoxes within MyCustomWidget to be styled in a certain way without affecting the rest of the QCheckBoxes in the application. I'd also like to be able to style them all at once and not have to name each single one and then make them have the same style.

I've tried to do it with something like:
MyCustomWidget::QCheckBox {
...
}
But that doesn't seem to work.

I've been looking at the QSS Styling Reference and I couldn't seem to find a solution to this particular problem.

Thanks in advanced
Cheerio

Code:

---

MyCustomWidget QCheckBox {
}

---

or if only direct children of MyCustomWidget (no intermediary container allowed)

Code:

---

MyCustomWidget > QCheckBox {
}

---

Cheers,
_