Toggle overlay with multiple choices

I am playing around with toggle overlay to open up a little help window for users.
If I have a field where they are supposed to fill in something, I added a little question mark image next to the field, where they can click and a little window opens up describing what it’s all about.

It works fine, but now I want to add questionmarks to other fields in the same window, opening up a different message. But, where should I add the code to make this work, so the script knwos what window is connected to what question mark?

I just found some code where I used copy and paste. So, I have no idea what it’s doing and why.

Here are the stuff I have from the head and body parts. But, as it is now, only the first description opens up when I click the question marks.
I need something to separate them or id them or whatever… but how?


<style type="text/css">
   div#overlay {
	display: none;
	z-index: 2;
	background: #000;
	position: fixed;
	width: 100%;
	height: 100%;
	top: 0px;
	left: 0px;
	text-align: center;
}
div#specialBox {
	display: none;
	position: relative;
	z-index: 3;
	margin: 150px auto 0px auto;
	width: 400px;
	height: 200px;
	background: #666;
	color: #000;
}
</style>

<div id="overlay"></div>
<div id="specialBox">
  <p>FIELD ONE<br />
  This field is for a description of field one.</p>
  <button onmousedown="toggleOverlay()">Close Overlay</button>
</div>

<div id="overlay"></div>
<div id="specialBox">
  <p>This is the second help window telling you what this is about.</p>
  <button onmousedown="toggleOverlay()">Close Overlay</button>
</div>

<p>FIELD ONE<img onmousedown="toggleOverlay()" src="./img/questionmark.gif" alt="example"><br />
<p>FIELD TWO<img onmousedown="toggleOverlay()" src="./img/questionmark.gif" alt="example"><br />

I found more code that I could modify. So, I will make it work now.