Issues with nesting CSS divs/boxes and overflow - css

Question

Hi I'm just wondering if anyone can help me out. I'm new enough to web design, and I'm having some problems with my CSS.
Basically I cant figure out how to correctly nest my divs/boxes without having overflow issues! I have tried using overflow: hidden; but this still hasn't worked, I've also tried floating the child elements either left or right to see if it would help but still no luck!
My css looks like this:
#customerReg {
width: 47%;
height: 480px;
float: left;
background: #FFF;
padding: 10px 10px 10px 10px;
display: inline;
margin-top: 10px;
-moz-border-radius: 20px;
-webkit-border-radius: 20px;
overflow: hidden;
}
#customerInfo {
width: 95%;
height: 120px;
background: #414141;
padding: 10px;
margin-bottom: 10px;
-moz-border-radius: 15px;
-webkit-border-radius: 15px;
overflow: hidden;
}
#participantReg {
width: 47%;
height: 480px;
float: right;
background: #FFF;
padding: 10px;
margin-top: 10px;
-moz-border-radius: 20px;
-webkit-border-radius: 20px;
overflow: hidden;
}
#participantInfo {
width: 95%;
height: 120px;
background: #414141;
padding: 10px;
margin-bottom: 10px;
-moz-border-radius: 15px;
-webkit-border-radius: 15px;
overflow: hidden;
}
My HTML Is as follows:
<div class="contentbody" style="border:#FF0066 solid 2px;">
<div id="customerReg" style="border:#33CC00 solid 2px">
<div id="customerInfo">
<p>Customer Registration
</p>
</div>
<!-- End of customerReg --></div>
<div id="participantReg" style="border:#33CC00 solid 2px">
<div id="participantInfo">
<p>Participant Sign Up</p>
<p> </p>
</div>
<!-- End of participantReg --></div>
<!-- end .contentbody --></div>
What im aiming for is so have two rounded boxes side by side with two smaller boxes inside these boxes. I tried to post an image but it wouldnt let me! What im getting is that the two inner boxes are both spilling out on the right side of the outer boxes if that makes sense??
Can anyone tell me where im going wrong and what i can do to correct this as ive spent hours trying to find an answer and cant figure it out!

Answer 1

The parent div set:
overflow: hidden;
OR
#customerReg, #participantReg{
float:left;
}
.contentbody:after{
content: '.';
clear:both;
visibility: hidden;
*zoom:1;
height:0;
display:block;
}

Answer 2

if you set the width of the first div the boxes ar side by side:
look this fiddle
.contentbody{
width:990px;
border:#FF0066 solid 2px;
}