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I checked and can see you have 6000+ lines of code in your child theme's style.css.
I am not sure how that happened. Please note that you don't have to copy everything from your parent theme.
You only need to add the codes that you need to override and everything else will be inherited.
I tried removing all the css code and the accordion works just fine.
Regretfully, this is outside the scope of support as this is not related to an issue with the theme and instead has to do with your customization of it.
Please check links below for your guide on how child theme works.
Thank you for your understanding.