Flexbox stretch textarea in column

Question

I am trying to get this textarea in a 2 column layout to stretch to fill the empty space. So the right column is variable height and I would like the textarea in the left column to stretch to fill the empty space. I have tried using align-items: stretch on the parent as well as setting the height to 100% on the textarea and I can't seem to get it to grow to fill the space.

Here is the HTML

<div class="row">
    <div class="left">
        <h1>Stuff</h1>
        <textarea></textarea>
    </div>
    <div class="right">
        <h1>Preview</h1>
        <div class="content"></div>
    </div>
</div>

Here are the styles

.row{
  display: flex;
  flex-direction: row;
  align-items: stretch;
  justify-content: space-between;
}

.row > div{
  flex: 0 0 50%;
  max-width: 50%;
}

textarea{
  height: 100%;
}

.content{
  height: 500px;
  background-color: green;
}

Here is a plunkr

I understand the need for vendor prefixes and all that so you don't need to get into that. This is just a simplified version of my code to demonstrate the problem I am having.

Answer 1

Make .left a flexbox, only allowing the textarea to grow:

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

.left > textarea {
  flex: 1;
}

Plunker