Creating a collapsible/accordion - Big Picture theme

Hi there - after no success with my bubble menu idea on a previous thread I’ve decided to try a simple collapsible or accordion style menu. I want the main buttons to be custom images that I upload through the HTML. When I try to enter the HTML and CSS, though, the button doesn’t work. The text that’s supposed to be hidden is visible, and clicking the button doesn’t do anything. Any thoughts?

Thank you!