How to make div same height as parent (displayed as table-cell)

Question

I got a container div containing three child divs (vary in content) - each as tall as the tallest one. I managed this by setting the container to display:table and the child divs to display:table-cell etc.

Everything worked just fine, until...

I inserted a new div inside one of the child divs and tried to make it height:100% - so it would stretch to the same height as its parents, but that did not work.

Please see my JSFiddle: http://jsfiddle.net/bkG5A/

Any help would be greatly appreciated!

HTML

<div class="container">
    <div class="child">
        a<br />a<br />a
    </div>
    <div class="child">
        a<br />a<br />a<br />a<br />a<br />a<br />a
    </div>
    <div class="child">
        <div class="content">
            a<br />a<br />a
        </div>
    </div>
</div>

CSS

.container {
    display: table;
}
.child {
    width: 30px;
    background-color: red;
    display: table-cell;
    vertical-align: top;
}
.content {
    height: 100%;
    background-color: blue;
}

Answer 1

Another option is to set your child div to display: inline-block;

.content {
    display: inline-block;
    height: 100%;
    width: 100%;
    background-color: blue;
}

.container {
  display: table;
}
.child {
  width: 30px;
  background-color: red;
  display: table-cell;
  vertical-align: top;
}
.content {
  display: inline-block;
  height: 100%;
  width: 100%;
  background-color: blue;
}

<div class="container">
  <div class="child">
    a
    <br />a
    <br />a
  </div>
  <div class="child">
    a
    <br />a
    <br />a
    <br />a
    <br />a
    <br />a
    <br />a
  </div>
  <div class="child">
    <div class="content">
      a
      <br />a
      <br />a
    </div>
  </div>
</div>

---

JSFiddle Demo