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问题:

ive got a problem on my position absolute property on IE7. My div moves 10px to the right. Below is my code. IE8 and 9 works fine. id menu is the div Im referring.

<!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" />
<style type="text/css">
body{margin: 0 0 0 0; padding: 0 0 0 0;}
#holder{width: 400px; height: 500px; margin: 0 auto;}
#left{float: left; width: 50px; height: 500px; background-color: red;}
#center{float: left; width: 300px; height: 500px; background-color: green;}
#right{float: left; width: 50px; height: 500px; background-color: red;}
#header{width: 300px; height: 70px; background-color: yellow;}
#gal-holder{width: 280px; height: 70px; margin: 0 auto;}
#gallery{width: 280px; height: 410px; background-color: orange;}
#button{width: 400px; height: 45px; background-color: red; margin: 0 auto;}
#menu{width: 300px; height: 45px; background-color: pink; position: absolute; z-index: 1000; top: 100px;}
#content{width: 380px; height: 200px; margin: 0 auto; background-color: blue; padding: 10px; color: #fff;}
#clear{height: 10px;}
</style>
</head>
<body>
<div id="holder">
    <div id="left"></div>
    <div id="center">
        <div id="header"></div>
        <div id="menu"></div>
        <div id="gal-holder">
            <div id="clear"></div>
            <div id="gallery"></div>
            <div id="clear"></div>
        </div>
    </div>
    <div id="right"></div>
</div>
<div id="button"></div>
<div id="content">Sample text</div>
</body>
</html>

回答1:

Add position:relative to #center and then left:0px to #menu.

Absolutely positioned elements are positioned relative to their closest positioned parent. It's best to give the items you want to position a left/right and top/bottom coordinate to prevent weird results like the one you found.

回答2:

You should specify both the top and left positions and add position:relative to the immediate parent:

#center {
    float: left;
    width: 300px;
    height: 500px;
    background-color: green;
    position:relative;
}
#menu { 
    width: 300px;
    height: 45px;
    background-color: pink;
    position: absolute;
    z-index: 1000;
    top: 100px;
    left: 0;
}

And a live example: http://jsfiddle.net/ambiguous/vRJMd/

The default left is auto and that more or less means that the browser can do whatever it thinks is sensible. Also, absolutely positioned elements are positioned with respect to the nearest ancestor with a position that is not static (which is probably <body> in your case).