The responsiveness of images side by side

Looking at it here:

How would I replicate that?

This is as far as I got:

It goes from this:

to this:

Using two individual images next to each other.

I don;t know what all that is but it just stacks one image on top of another.

I would do something simple like this:

Yes that live site is horrible and uses the picture element and js to change and re-position the image. Its very jerky when I resize my browser and I don’t like it at all. Why put all that effort in making something worse?