That's correct - no Js used in this project recreation (though I'm always keen on learning from experienced practitioners!).
Sure! I am using the term "contrast" loosely to refer to visual changes that occur when moving through the app. For example, currently, the "Start," "Post," and "Post a different comment" buttons all have a static look that could benefit from a Hover and Selected state, much like the one's you've employed for the four comment choices. Case in point, I applied a Hover state to the aforementioned buttons, while also giving the "Post" button a Disabled state to communicate to the user that a selection must be made before "posting." I also found the Feedback layer/slide itself could benefit from a "layer/slide title" and darker background to help distinguish itself from the other areas of the interaction.