Image priority when site dynamically resizes

The OneMag.us site is shared on the SquareSpace inspiration page, and I really love how the landing page works, but can't figure out how to replicate it.

When fullscreen on my computer, or horizontal orientation on my iphone, the page is split down the middle with two images filling the screen.  Simple enough.  But what I really like is when the screen is resized, at a certain point the images stop downsizing and the image on the right takes priority while the left image is pushed offscreen.  (On the phone when the screen is turned to vertical orientation the image on the right takes over and the image on the left disappears instead of just getting pushed below the other image.

Does this require additional code?  Can it be achieved through Fluid Engine (that's what I'm using).

In general, being able to "hide" a block or a section in mobile view would be very useful.

Thanks.