// This is the event "onscroll" on the window object, that we're binding to and passing an
// anonymous function as the function to be executed when the event is triggered
    window.onscroll = function (event) {
      // Then here (inside the anonymous function that's being passed in), we add the class
      // "my-class" to the document body.
      document.body.classList.add("my-class");
    }