Flex children not expanding to full height

Issue

I have a dynamic footer on my page and I expect the content above it to scale to reach the top of the footer, that's fine and all, but I'm having a problem:

#snippet-container {
  height: 300px;
  width: 200px;
}

#page {
  display: flex;
  flex-flow: column;
  height: 100%;
}

#content {
  flex: 1 1 auto;
  background: blue;
}

#content .test {
  width: 100%;
  height: 100%;
  background: yellow;
  border: 2px solid red;
}

#footer {
  flex: 0 1 10vh;
  background: black;
}

<div id="snippet-container">
  <div id="page">
    <div id="content">
      <div class="test"></div>
    </div>
    <div id="footer"></div>
  </div>
</div>

I would expect the .test element to fill the #content element, hence the 100%/100% width/height however it does not.

You can see this reflected as I gave the .test element a red border in the snippet.

Solution

PROBLEM:

The problem is that your #page flex container is not reaching the .test element since .test is not a child, it is a descendant of the flex item.

The contents of a flex container consists of zero or more flex items: each child of a flex container becomes a flex item.

Each flex item is affected by the flex container, but the flex item's descendants are not.

---

SOLUTION:

You need to add display: flex to your #content as well.

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JSFiddle

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CODE SNIPPET:

#snippet-container {
  height: 300px;
  width: 200px;
}
#page {
  display: flex;
  flex-flow: column;
  height: 100%;
}
#content {
  display: flex;
  height: 100%;
  background: blue;
}
#content .test {
  width: 100%;
  background: yellow;
  border: 2px solid red;
}
#footer {
  flex: 0 1 10vh;
  background: black;
}

<div id="snippet-container">
  <div id="page">
    <div id="content">
      <div class="test"></div>
    </div>
    <div id="footer"></div>
  </div>
</div>

Answered By - Ricky