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

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;
}

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;
}