Use an existing checkbox to change a parent style

Hello,
I am trying to override a plugin's CSS on a quiz, so that when the user checks the box, the background color changes.

The quiz is here:
http://kocher.co/quizzes/test-quiz-lesson-01/

I have tried everything I can think of, including:
'input.wpProQuiz_questionInput:checked + .wpProQuiz_questionList[data-type="multiple"] {
background: pink !important;
}'

I'm obviously no design guru, but any help would be greatly appreshaited. If CSS can't do this, is there a simple way to do it with Jquery?

Thanks so much!!