A negative value places element below the normal flow, and a positive value places them above the flow. : z index : Box Model HTML CSS TUTORIALS

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A negative value places element below the normal flow, and a positive value places them above the flow.


 
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
<head>
<title>Z-Axis Positioning</title>
<style type="text/css">
#bottom {
position: absolute;
left: 100px;
top: 25px;
z-index: 1;
border: 1px solid black;
}
#middle {
position: absolute;
left: 90px;
top: 25px;
z-index: 2;
border: 1px dotted red;
}
#top {
position: absolute;
left: 80px;
top: 25px;
z-index: 3;
border: 1px dashed green;
}
</style>
</head>
<body>
<div id="top"><img src="white.gif" width="300" height="300" alt=""
border="0"></div>
<div id="middle"><img src="white.gif" width="300" height="300" alt=""
border="0"></div>
<div id="bottom"><img src="white.gif" width="300" height="300" alt=""
border="0"></div>
</body>
</html>