How to change the "down-button" in QDateEdit with CalendarPopup?

Question

I want to change the dropdown button in my QDateEdit but nothing works.

with:

QDateEdit::down-arrow{  
    height:12px;
    width:12px;
    image:url('://Assets/chevron-down-dark.png');
}

i can change the little down-arrow-icon but if use this:

QDateEdit::down-button{ 
    height:12px;
    width:12px;
    image:url('://Assets/chevron-down-dark.png');
 }

so down-button instead of down-arrow, nothing happens. In other QSpinBoxes this works for me but not in QDateEdit.