When using float: left or right in Child divs, make sure to add position: relative to them. And add overflow: hidden in their Parent div. The Parent div will inherit the height of his Child divs. The code below will show you want I mean.

 

<style type="text/css">
.body {
background-color: #000;
height: auto;
position: relative;
overflow: hidden;
width: 500px;
}
.left {
background-color: #00F;
float: left;
height: 400px;
position: relative;
width: 200px;
}
.right {
background-color: #F00;
float: right;
height: 600px;
position: relative;
width: 300px;
}
</style>
<div class="body">
 <div class="left"></div>
 <div class="right"></div>
</div>

 

Try this, u have to clear after floating for arranging other elements. Lots of way the clear, i just giving the easy one.

<div class="body">
  <div class="left"></div>
  <div class="right"></div>
<div style="clear: both;"></div>
</div>