I have this **[JSFIDDLE](https://jsfiddle.net/qrsotzpr/2/)** with a parallax effect on my images. 
The problem is that I have two scrollbars in the result. 
How can I have only one scrollbar for all my content ?

HTML : 

```
<div id="intro">
<p>Sed uelit, sed quia...</p>
</div>

<div id="text">
<h1>Hello</h1>
</div>
<div id="wrapper">
    <section id="frame1">
        <div class="back">
        </div>
    </section>

        <section id="frame7">
        <div class="back">

        </div>
    </section>

</div>

```