html - flex child is growing out of parent

Question

How to force the green boxes to be contained in the red one without setting a static height value and no absolute position?

I want to shrink the content to fit into the parent.

The content (video in this case) is allowed to shrink and scrollbars are allowed.

.my-box {
  height: 300px;
  width: 600px;
  background: red;
  padding: 5px;
}
.content-box {
  background: blue;
}
.col {
  display: flex;
  flex-direction: column;
  justify-content: space-between
}
.box-shrink {
  flex: 0 1 auto;
  background: green;
  padding: 5px;
  margin: 5px;
}
.box-grow {
  flex: 1 0 auto;
  background: green;
  padding: 5px;
  margin: 5px;
}
video {
  max-height: 100%;
  max-width: 100%;
  margin: auto;
  display: block;
}

<div class="my-box col">
  <div class="box-shrink">
    small sized static content
  </div>
  <div class="content-box box-grow">
    <video controls>
      <source src="http://techslides.com/demos/sample-videos/small.webm" type="video/webm">
    </video>
  </div>
  <div class="box-shrink">
    small sized static content
  </div>
</div>

Answer 1

Solution #1 - Without Scroll

Instead of flex: 1 0 auto on the video container, just use flex: 1. This sizes the item based on available space, not the intrinsic height of the content.

Then, because flex items cannot be smaller than the size of their content – min-height: auto is the default – add min-height: 0 to allow the item to shrink to fit inside the container.

.box-grow {
  flex: 1; /* formerly flex: 1 0 auto; */
  background: green;
  padding: 5px;
  margin: 5px;
  min-height: 0; /* new */
}

.my-box {
  height: 300px;
  width: 600px;
  background: red;
  padding: 5px;
}
.content-box {
  background: blue;
}
.col {
  display: flex;
  flex-direction: column;
  justify-content: space-between
}
.box-shrink {
  flex: 0 1 auto;
  background: green;
  padding: 5px;
  margin: 5px;
}
.box-grow {
  flex: 1; /* formerly flex: 1 0 auto; */
  background: green;
  padding: 5px;
  margin: 5px;
  min-height: 0; /* new */
}
video {
  max-height: 100%;
  max-width: 100%;
  margin: auto;
  display: block;
}

<div class="my-box col">
  <div class="box-shrink">
    small sized static content
  </div>
  <div class="content-box box-grow">
    <video controls>
      <source src="http://techslides.com/demos/sample-videos/small.webm" type="video/webm">
    </video>
  </div>
  <div class="box-shrink">
    small sized static content
  </div>
</div>