Please, make sure that classnames that you are using on the page structure are the same that you added in the code snippet.
Right now this difference causing the error:
In the code from the tutorial I used the “underscore” and in the classname that you applied to the div there is a “dash”. It make those 2 are totally different classnames and plugin doesn’t work.
Change the classname either in the code or on the div and I think it should be fine.