I am trying to make the outer class - `rightholder_empty`, expand vertically with the content of the inner classes but have run out of ideas...If you can help, could you please explain too as I need to understand this.

**The HTML & CSS:**

```
<html>
<head>
<title>Css test</title>
<style>
  .rightholder_empty {
    padding:15px;
    margin:0 auto;
    border: solid 6px #e8e8e8;
    background: #f5f5f5;
    -webkit-box-shadow: 0 8px 6px -6px #666;
    -moz-box-shadow: 0 8px 6px -6px #666;
    box-shadow: 0 8px 6px -6px #666;
    border-radius:4px;
    position:relative;
    width:700px;
}

.split_l {
    padding:15px;
    margin-bottom:10px;
    background: #f5f5f5;
    float:left;
    width:45%;
    position:relative;
}

.split_r {
    padding:0 15px 15px 15px;
    margin-bottom:10px;
    background: #f5f5f5;
    float:right;
    width:45%;
    border-left: solid 4px #ededed;
    position:relative;
}

</style>
</head>

<body>

<div class="rightholder_empty">
    <div class="split_l">hello<br /><br />h<br /><br />h<br /><br />h</div>
    <div class="split_r">world</div>
</div>

</body>
</html>

```