Fixed div modal not scrolling with page - css

Question

I have a html/css modal on my page which is hosted here:
http://yousolutions.co.za/#openModalViewCreateClient
However, I need to be able to use the main scroller on the page to scroll down and view the rest of this form. My current CSS doesn't allow for this, and I don't want to add another scroll bar within the div. My code looks like this:
HTML:
<div id="openModalViewCreateClient" class="modalDialog">
<div>
X
<h2>Add A Client</h2>
<form class="contact_form" action="#" method="post" name="contact_form">
<ul>
<li>
<h2>Add New Client</h2>
</li>
<li>
<label for="name">First Name:</label>
<input type="text" placeholder="John" required />
</li>
<li>
<label for="name">Last Name:</label>
<input type="text" placeholder="Doe" required />
</li>
<li>
<label for="email">Email:</label>
<input type="email" name="email" placeholder="john_doe#example.com" required />
<span class="form_hint">Proper format "name#something.com"</span>
</li>
<li>
<label for="website">Website:</label>
<input type="url" name="website" placeholder="http://johndoe.com" required pattern="(http|https)://.+"/>
<span class="form_hint">Proper format "http://someaddress.com"</span>
</li>
<li>
<label for="message">Message:</label>
<textarea name="message" cols="40" rows="6" required ></textarea>
</li>
<li>
<button class="submit" type="submit">Submit Form</button>
</li>
</ul>
</form>
</div>
</div>
CSS:
.modalDialog:target {
opacity:1;
pointer-events: auto;
}
.modalDialog {
position: fixed;
font-family: Arial, Helvetica, sans-serif;
top: 0;
right: 0;
bottom: 0;
left: 0;
background: rgba(0,0,0,0.8);
z-index: 99999;
opacity:0;
-webkit-transition: opacity 400ms ease-in;
-moz-transition: opacity 400ms ease-in;
transition: opacity 400ms ease-in;
pointer-events: none;
}
.modalDialog > div {
width: 630px;
position: relative;
margin: 10% auto;
padding: 5px 20px 13px 20px;
border-radius: 10px;
background: #fff;
background: -moz-linear-gradient(#fff, #999);
background: -webkit-linear-gradient(#fff, #999);
background: -o-linear-gradient(#fff, #999);
}
.close {
background: #606061;
color: #FFFFFF;
line-height: 25px;
position: absolute;
right: -12px;
text-align: center;
top: -10px;
width: 24px;
text-decoration: none;
font-weight: bold;
-webkit-border-radius: 12px;
-moz-border-radius: 12px;
border-radius: 12px;
-moz-box-shadow: 1px 1px 3px #000;
-webkit-box-shadow: 1px 1px 3px #000;
box-shadow: 1px 1px 3px #000;
}
.close:hover { background: #00d9ff; }

Answer 1

You are using
position: fixed;
on .modalDialog, the viewport scrolling does not have any effect in this case on the modal
Try with absolute positioning -
position: absolute;