Running code in ws3 vs running it like .html extension

[emivynck]

Hey, for a webpage I would like to use collapsibles. I searched how to make this and found a solution on ws3 schools. When I applied it to my case and tried  running it in ws3 schools it worked. But when i copy the code into a txt file, and then save it as a .html file and run it, the collapsibles don't work. Does anybody know what I'm doing wrong? When you run the code in ws3 it works fine.

html.txt

[Funce]

This collapses just fine. Which tutorial are you trying this on?