applying `:after` CCS pseudo to one element of a carousel affects all elements

When applying `:after` CCS pseudo to one element of a carousel, it affects all elements.
Example: https://codesandbox.io/s/react-slick-playground-lweop?file=/index.css

When inspecting the structure, the `after` seems to be correctly attached to just the desired slide.

producing the desired effect.

However, other slides are also being affected by that `after`, which is not the intention.