CSS Floating with Overlap
I'm trying to set up a simple horizontal tab structure for a page I'm working on, and I'm running into some trouble with floating div's combined with z-index.
Viewing the following code in a browser:
<!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">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Untitled Document</title>
<style type="text/css">
#main { width: 500px; z-index: 1;}
.left { float: left; width: 96px; background-color: red; border: 2px solid orange; z-index: 2; margin-right: -2px }
.right { float: left; width: 396px; background-color: #09c; border: 2px solid green; z-index: 3; }
.clear { clear: both; }
</style>
</head>
<body>
<div id="main">
<div class="left">
LEFT
</div>
<div class="right">
RIGHT
<br />
RIGHT
</div>
<div class="clear"></div>
</div>
</body>
</html>
Why doesn't the left div's orange border overlap the right div's green border?
Answer
z-index property will not apply to statically positioned elements. In order to use z-index the CSS must also include any position value other than static (ie relative, absolute, fixed).
.left { float: left; width: 96px; background-color: red; border: 2px solid orange; z-index: 3; margin-right: -2px; position: relative; }
.right { float: left; width: 396px; background-color: #09c; border: 2px solid green; z-index: 2; position: relative; }
Will give you what you want I think. I added position: relative; and changed the z-index of the .left to 3 (from 2) and changed the z-index of .right to 2 (from 3).