51help TIY
码：
<html> <head> <style type="text/css"> #img1 { position:absolute; left:0px; top:0px; z-index:-1 } </style> <script type="text/javascript"> function changeStackOrder() { document.getElementById("img1").style.zIndex="1"; } </script> </head> <body> <h1>This is a Heading</h1> <img id="img1" src="../i/eg_bulbon.gif" tppabs="http://www.51help.tk/i/eg_bulbon.gif"> <p>Default z-index is 0. Z-index -1 has lower priority.</p> <input type="button" onclick="changeStackOrder()" value="Change stack order" /> </body> </html>
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