Flexbox 3 divs, two columns, one with two rows

Question

I am trying to take

Three sequential divs and turn it into below. W

Answer 1

After thinking about this a little more, it is possible with flexbox. The container just has to have a defined height (%, px or vh) will work.

http://codeply.com/go/U1DCKAx85d

body {
  display: flex;
  flex-wrap: wrap;
  flex-direction: column;
  height: 100vh;
}

.a {
  flex: 0 0 100%;
  background: red;
}

.b, .c {
  flex: 0 0 50%;
  background: green;
}

.c {
  background: blue;
}

Answer 2

The Legit Method:
*Recommended

.flex-row {
    flex-direction: row;
    display: flex;
}

.flex-column {
    flex-direction: column;
    display: flex;
}

.flex-body {
    display: flex;
}

.flex-body div:not([class*="flex"]) {
    border: 1px solid white;
    flex: 1 1 200px;
    width: 300px;
}

<div class="flex-body">
  <div class="flex-row">
    <div style="background: #0980cc;"></div>
  </div>
  <div class="flex-column">
    <div style="background: #09cc69;"></div>
    <div style="background: #cc092f;"></div>
  </div>
</div>

The Hackish Method:
*Not Recommended (I'm sure you'll notice why)

.flex-body {
    display: flex;
    flex-direction: row-reverse;
    flex-wrap: wrap;
    justify-content: flex-end;
    align-content: stretch;
    align-items: stretch;
    transform: rotate(90deg);
    max-width: 500px;
    margin: auto;
}

.flex-body div {
    border: 1px solid white;
    height: 300px;
    flex: 1 1 200px;
}

.flex-body div:last-of-type {
    flex: 1 1 300px;
    height: 300px;
}

<div class="flex-body">
  <div style="background: #0980cc;"></div>
  <div style="background: #09cc69;"></div>
  <div style="background: #cc092f;"></div>
</div>