Adding Scroll Animation Problem

Hi,

I am trying to follow the steps in this video (https://www.youtube.com/watch?v=05frGyjyZvE) to create a horizontally scrolling web page.

For this I need to add a scroll animation to my website. When I go to add a scroll animation however, I cannot seem to

.

When I try to click on the little cross button in the top right hand corner of the image here, nothing happens, no matter how many times I refresh the page or close the window and open it again.

Is there something that needs to come before this step?

Thanks in advance.