In this example there is a horizontal scroll and when a button (filter) is clicked it reloads the page.

How would one implement something like this. There is a horizontal scroll but the active one is always in view. I inspected this and there does not seem to be any css doing this, it looks like pure javascript.

In the image below we can see denim is the 9th li item and has a class active, but I don't get how they have it so it's always in view when an item is clicked and the page reloads.

Here is a link to an example: https://www.prada.com/us/en/women/bags/top_handles.html