Change flex direction on wrap

Question

I am trying to use a nested flexbox layout in order to achieve the following layout when there is a certain amount of space:

Then, when there isn't enough space, the right-hand side should wrap to a row layout instead of a column layout, so that the boxes are side-by-side when they wrap, example:

The idea is to have the boxes on the right 50% of the left content so that when they wrap underneath, they are the same combined size as the left content.

However, I can't figure out how to do this via flexbox only. This is what I have so far, but if you resize the window you'll see that the boxes stay in the same direction:

http://jsfiddle.net/usLxshro/

div {
    min-height: 50px;
    background: #E7E7E7;
    margin: 10px;
}
#wrapper {
    display: flex;
    flex-wrap: wrap;
}
#left-content {
    flex: 2;
    min-width: 200px;
}
#right-content {
    flex: 1;
    min-width: 200px;
}
section {
    border: 1px solid #333;
    margin: 10px;
}

Answer 1

You can use media-queries to change behavior

@media (max-width: 500px) {
    #wrapper {
        flex-direction: column;    
    }
    #right-content {
        display: flex;
    }

    section {
        flex: 1;   
    }
}

See updated fiddle — http://jsfiddle.net/shurshilin/usLxshro/1/

Hope it'll help you.