Responsive Boxes

Hi!!

I’m having some trouble with making some responsive boxes. They’re like this:

In small screens I want the pink box to go under the black box, but they’re like this:

Here’s the code i’m using:
image

So you want two pink boxes under each other and then the black boxes like:

?

I want just like this:

but just in small screens!

In big screens I want to let them stay where they are.