Markdown Titles not collapsing (what code do I need to delete on css)

 As seen on most my tabs of my website, the markdown title blocks aren't collapsing. 

Would someone please help me with this and find what code on CSS I need to delete? An example of my website:
https://www.secret-valley.co.uk/glamping-holidays-in-somerset

Thanks so much from a struggling farmer!
Will 

I think they are working, but they contain no content, just a heading.

Have you tried using the accordion block?

https://support.squarespace.com/hc/en-us/articles/4411581892749-Accordion-blocks