Thanks @Richard, it's finally working! Besides adding a height property to "panel" I just had to add to the paragraph a class like "_Quote". Without a class the "<p>Lorem ipsum...</p>" wasn't working, so adding it makes it work even as in the bottom:
<p class="_Quote">Lorem ipsum...</p>
Hi! I'm having the same problem here with the code provided by @Richard. The accordion is only working in right way if you use it in the bottom page html. If you use it inside the composer with "+ html" the accordion buttons appear but nothing happens when you click them.
Adding a a height property in CSS to the panel doesn't seem to work either.