Ok - I have the code I need. Just a small amount of JavaScript. I have inserted a SEWP on my modal dialog page with the below code to close this window.
The link above to my previous code I have a page that onload launches a modal dialog. I wanted to hide the close button and add a new button which would close the dialog.
<script language="javascript" type="text/javascript">
function closePopup() {
window.frameElement.cancelPopUp();
return false;
}
</script>
<div id="confirmBut" style="margin:0;">
<input onclick="closePopup();" title="Close this message" type="button"
value="Click here to confirm you accept and understand this message"
style="margin: 0; border-radius:5px; width:500px; height:50px;
background-color:red; border: 1px grooved grey; font-size:16px;
color:white; font-weight:bold; cursor:pointer;">
</div>
I know I am able to put the css on the button elsewhere but I have popped it on the item.