Need to fix div when scrolling stay 20px from top

Question

I am not sure wether this can be done with pure CSS or if I need to use some jQuery to do this.

I have a div (product_image) that in its current state sits at about 400px from the top and positioned relative so it clears the top menu and header, what I need to do is when a user scrolls down and gets to about 20px from the top of the div, I need the div to become fixed.

Here's what I have tried, I have the main div with relative positioning then I have another div wrapping everything inside with fixed positioning. The problem is that the div is staying put at 400px from the top.

Here's the code:

<div class="product_image">
    <div class="product_image_fixed">
    <a href="products/1.jpg" class="zoom" title="A bed!" rel="gal1">  
        <img src="products/1.jpg" width="450" alt="" title="A bed!">  
    </a>

    <ul id="thumblist" class="clearfix" >
        <li><a class="zoomThumbActive" href='javascript:void(0);' rel="{gallery: 'gal1', smallimage: 'products/1.jpg',largeimage: 'products/1.jpg'}"><img src='products/1.jpg' width="150" height="100"></a></li>
        <li><a href='javascript:void(0);' rel="{gallery: 'gal1', smallimage: 'products/1a.jpg',largeimage: 'products/1a.jpg'}"><img src='products/1a.jpg' width="150" height="100"></a></li>    </ul>
    </div>
    </div> 

And the CSS

.product_image {
    position: relative;
    float: left;
    width: 450px;
    margin-left: 10px;
    margin-top: 10px;
}

.product_image_fixed {
    position: fixed;
    float: left;
}

I hope I have made the question clear enough, I can't seem to find a solution to this around so I thank you in advance for your help!

Answer 1

Used to jquery

Jquery

$(document).ready(function() {
    var s = $("#sticker");
    var pos = s.position();                    
    $(window).scroll(function() {
        var windowpos = $(window).scrollTop();

        if (windowpos >= pos.top) {
            s.addClass("stick");
        } else {
            s.removeClass("stick"); 
        }
    });
});

Css

div#wrapper {
    margin:0 auto;
    width:500px;
    background:#FFF;
}
div#mainContent {
    width:160px;
    padding:20px;
    float:left;
}
div#sideBar {
    width:130px;
    padding:20px;
    margin-left:30px;
    float:left;
}
.clear { 
    clear:both; 
}
div#sticker {
    padding:20px;
    margin:20px 0;
    background:#AAA;
    width:190px;
}
.stick {
    position:fixed;
    top:0px;
}

HTML

<div id="wrapper">
  <div id="mainContent">
      some content here <br />
       some content here <br />
       some content here <br />
       some content here <br />
       some content here <br />
      some content here <br />
       some content here <br />
       some content here <br />
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       some content here <br />
      some content here <br />
       some content here <br />
       some content here <br />
       some content here <br />
       some content here <br />
      some content here <br />
       some content here <br />
       some content here <br />
       some content here <br />
       some content here <br />
      some content here <br />
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      some content here <br />
       some content here <br />
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      some content here <br />
       some content here <br />
       some content here <br />
       some content here <br />
       some content here <br />
  </div>
  <div id="sideBar">Some content here 
    <!--Some content in your right column/sidebar-->
    <div id="sticker">...This is scroll here </div>
  </div>
  <div class="clear"></div>
</div>

Demo

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