CSS: How to custom hover as seen on Product Hunt card items

The Problem

On Product Hunt, when hovering over a card, it changes the colour to a darker grey. Then, when you reach the comment box, it changes the card back to white, but now changes the comment box to the darker grey (as seen in the image below).

How does the rest of the card return back to its normal colour when you hover over the comment box?

What I've Tried

As an intro-level CSS and web dev, I initially thought it was the z-index, but it was not. Does anyone have an idea as to how you can do this?

Thanks in advance, any help is appreciated 🙂