JavaFX how to style the button part of a checkbox?

I am trying to do some css styling in a stylesheet for a JavaFX scene. It is going to be loaded upon opening the scene, and targets all the "basic" elements of a scene.

My problem is that i can't seem to find the right combination of code, to change the background color, of the button in a standard JavaFX checkbox.

This is where i am now:

.check-box:selected{
    -fx-background-color: #00FF00;
}

I have tried some variants of the above, like

.check-box .button{
    -fx-fill: #00FF00;
    -fx-background-color: #00FF00;
}

and others, but without success.

So in general, how do i access a button in a checkbox?

Thank you in advance :-)