Hiding the next button using css for only a particular div class?

Hello,
I need to hide the "next button" in one question but without using javascript feature. I am thinking to use CSS to hide the button.
I can declare the whole intended question under the div with say class = "case-xyz". Something like this in the HTML pane.

But now when I want to define the custom css for "case-xyz", I am trying something like-
.case-xyz #NextButton{display: none;} OR
#NextButton .case-xyz{display:none}
but it's not working and I am not sure how to combine class and id selector here.
How to select the next button for a question defined under certain div with a class?