JS 实现div 居中显示

<!DOCTYPE html> 
<html> 
<head> 
<meta charset="utf-8" /> 
<title>JS实现div居中</title> 

<style> 
    /*外层div居中*/ 
    #main { 
        position: absolute; /*极为重要*/ 
        background-color: blue; 
        width:400px; 
        height:200px; 
        /*left:50%; 
        top:50%; 
        margin-left:-200px; 
        margin-top:-100px;*/ 
        border:1px solid #00F; 
    } 

    #content { 
        position: absolute; /*极为重要*/ 
        background-color: yellow; 
        width: 200px; 
        height: 100px; 
        /*left:50%; 
        top:50%; 
        margin-left:-100px; 
        margin-top:-50px;*/ 

        /*div内部文字居中*/ 
        text-align: center; 
        line-height:100px; /*行间距和div宽度相同*/ 
    } 
</style> 
<body> 
    <div id="main"> 
        <div id="content"> 
            Sun 
        </div> 
    </div> 
    <script type="text/javascript"> 
        window.onload = function() { 
        // 获取浏览器窗口 
        var windowScreen = document.documentElement; 
        // 获取main的div元素 
        var main_div = document.getElementById("main"); 
        // 通过窗口宽高和div宽高计算位置 
        var main_left = (windowScreen.clientWidth - main_div.clientWidth)/2 + "px"; 
        var main_top = (windowScreen.clientHeight - main_div.clientHeight)/2 + "px"; 
        // 位置赋值 
        main_div.style.left = main_left; 
        main_div.style.top = main_top; 

        // 获取mcontent的div元素 
        var content_div = document.getElementById("content"); 
        var content_left = (main_div.clientWidth - content_div.clientWidth)/2 + "px"; 
        var content_top = (main_div.clientHeight - content_div.clientHeight)/2 + "px"; 
        content_div.style.left = content_left; 
        content_div.style.top = content_top; 

        } 
    </script> 
</body> 
</html>
JS 实现div 居中显示

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