height:100% not working inside flexbox with flex-grow

Question

The blue box should be 100% height. It works when I set a pixel height for div.a, but unfortunately this is not an option for the real world case.

This probably explains everything: http://codepen.io/anon/pen/jrVEpB

.a{
  background-color:red;
  display:flex;
}
.b1{
  flex-grow:0;
  background-color:green;
}
.b2{
  flex-grow:1;
  background-color:yellow;
  height:100%;
}

.c{
  height:100%;
  background-color:blue;
}

<div class="a">
  <div class="b1">
    <p>hurr durr</p>
    <p>hurr durr</p>
    <p>hurr durr</p>
    <p>hurr durr</p>
    <p>hurr durr</p>
    <p>hurr durr</p>
    
  </div>
  <div class="b2">
      <div class="c">
          miksi et ole full height saatana
      </div>
  </div>
</div>

Answer 1

You don't need percentage heights to achieve this layout. It can be built with flex properties alone:

.a {
  display: flex; 
  background-color: red;
}
.b1 {
  background-color: green;
}
.b2 {
  flex: 1;
  display: flex;
  background-color: yellow;
}
.c {
  flex: 1;
  background-color: blue;
}

body { margin: 0; }

<div class="a">
  <div class="b1">
    <p>hurr durr</p>
    <p>hurr durr</p>
    <p>hurr durr</p>
    <p>hurr durr</p>
    <p>hurr durr</p>
    <p>hurr durr</p>
  </div>
  <div class="b2">
    <div class="c">
      miksi et ole full height saatana
    </div>
  </div>
</div>

If using percentage heights is a must, then consider the proper implementation:

• Working with the CSS height property and percentage values
• Chrome / Safari not filling 100% height of flex parent