Flexbox Sticky Footer - 'Flex: 1' Not Working to Fill Height

I'm trying to test out the flexbox sticky footer method at the moment for a dynamic-height footer, something I've had problems with for a while, but I'm having trouble with the main section not expanding to fill the full height of the window using 'flex: 1', after applying 'min-height: 100vh' and 'flex-direction: column' to the containing body.

This is leaving the footer still half way up the page and I can't figure out after reading up on it why this shouldn't be working.

HTML:

    <body>

    <div id="wrapper">

        <main>

            <div id="pageContent">

                <h1>Page Content</h1>

                <h2>Page Content</h2>

                <h3>Page Content</h3>

                <h4>Page Content</h4>

            </div>

        </main>

        <footer>

            <row>

                <p>Footer Content</p>

                <p>Footer Content</p>

                <p>Footer Content</p>

                <p>Footer Content</p>

            </row>

        </footer>

    </div>

</body>

CSS:

html, body
{
margin: 0;
padding: 0;
max-width: 100%;
background: #1a1a1a;
}

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

main
{
width: 100%;
margin: 0;
padding: 50px 10%;
box-sizing: border-box;
-webkit-box-sizing: border-box;
-moz-box-sizing: border-box;
flex: 1;
}

main > #pageContent
{
height: 100%;
width: 100%;
margin: 0;
}

footer
{
height: auto;
background: #0d0d0d;
padding: 0 10%;
margin: 0;
}

footer > row
{
display: flex;
}

footer > row > p
{
flex-grow: 1;
flex-basis: 0;
text-align: center;
padding: 25px 0;
margin: 0;
}

Solution

You haven't applied display:flex to the #wrapper div.

Flexbox is not inherited.

html,
body {
  margin: 0;
  padding: 0;
  max-width: 100%;
}
body {
  display: flex;
  min-height: 100vh;
  flex-direction: column;
}
#wrapper {
  flex: 1;
  display: flex;
  flex-direction: column;
}
main {
  width: 100%;
  margin: 0;
  padding: 50px 10%;
  box-sizing: border-box;
  -webkit-box-sizing: border-box;
  -moz-box-sizing: border-box;
  flex: 1;
}
main > #pageContent {
  height: 100%;
  width: 100%;
  margin: 0;
}
footer {
  height: auto;
  background: lightgreen;
  padding: 0 10%;
  margin-top: auto;
}
footer > row {
  display: flex;
}
footer > row > p {
  flex-grow: 1;
  flex-basis: 0;
  text-align: center;
  padding: 25px 0;
  margin: 0;
}

<div id="wrapper">

  <main>

    <div id="pageContent">

      <h1>Page Content</h1>

      <h2>Page Content</h2>

      <h3>Page Content</h3>

      <h4>Page Content</h4>

    </div>

  </main>

  <footer>

    <row>

      <p>Footer Content</p>

      <p>Footer Content</p>

      <p>Footer Content</p>

      <p>Footer Content</p>

    </row>

  </footer>

</div>

Codepen Demo