accordeoniste

I wish to create popup descriptions for my website. I followed the example on W3Schools' "How to Create Popups" page at https://w3schools.com/howto/howto_js_popup.asp. The example included Javascript code. However, the popup didn't work on my site as it did in the example. A script error message appeared saying "unable to get property 'toggle' of undefined or null reference". I looked for a Javascript function in the page source code that would refer to the toggle script, but couldn't find one. I don't know Javascript so I need a little help supplying the requisite function. Can someone help?