实现DIV居中的几种方法

<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title>demo</title>
    </head>
    <body>
        <style type="text/css">
            .div1{  width: 100px; height: 100px; border: 1px solid #000000;}
            .div2{ width:40px ; height: 40px; background-color: green;}
        </style>

        <div class="div1">
            <div class="div2">

            </div>
        </div>

    </body>
</html>

如上的两个div，实现div2在div1里面是居中显示

一、方法一

　　利用margin，div1的宽减去div2的宽就是div2margin-left的数值：（100-40）/2=30

　　div1的高减去div2的高就是div2margin-top的数值：（100-40）/2=30

<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title>demo</title>
    </head>
    <body>
        <style type="text/css">
            .div1{  width: 100px; height: 100px; border: 1px solid #000000;}
            .div2{ width:40px ; height: 40px; background-color: green;}

            .div22{
                margin-left: 30px;margin-top: 30px;
            }
        </style>

        <div class="div1">
            <div class="div2 div22">

            </div>
        </div>

    </body>
</html>

二、方法二

　　利用css的 position属性，把div2相对于div1的top、left都设置为50%，然后再用margin-top设置为div2的高度的负一半拉回来，用marg-left设置为宽度的负一半拉回来，css如下设置

<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title>demo</title>
    </head>
    <body>
        <style type="text/css">
            .div1{  width: 100px; height: 100px; border: 1px solid #000000;}
            .div2{ width:40px ; height: 40px; background-color: green;}

            .div11{
                position: relative;
            }
            .div22{
                position: absolute;top:50%;left: 50%;margin-top: -20px;margin-left: -20px;
            }
        </style>

        <div class="div1 div11">
            <div class="div2 div22">

            </div>
        </div>

    </body>
</html>

三、方法三

　　还是用css的position属性，如下的html

<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title>demo</title>
    </head>
    <body>
        <style type="text/css">
            .div1{  width: 100px; height: 100px; border: 1px solid #000000;}
            .div2{ width:40px ; height: 40px; background-color: green;}

            .div11{
                position: relative;
            }
            .div22{
                position: absolute;margin:auto; top: 0;left: 0;right: 0;bottom: 0;
            }
        </style>

        <div class="div1 div11">
            <div class="div2 div22">

            </div>
        </div>

    </body>
</html>

四、方法四

　　利用css3的新增属性table-cell

<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title>demo</title>
    </head>
    <body>
        <style type="text/css">
            .div1{  width: 100px; height: 100px; border: 1px solid #000000;}
            .div2{ width:40px ; height: 40px; background-color: green;}

            .div11{
                display: table-cell;vertical-align: middle;
            }
            .div22{
                margin: auto;
            }
        </style>

        <div class="div1 div11">
            <div class="div2 div22">
            </div>
        </div>

    </body>
</html>

这个方法还有一个好处就是，div2的高度可以不固定，如下

<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title>demo</title>
    </head>
    <body>
        <style type="text/css">
            .div1{  width: 100px; height: 100px; border: 1px solid #000000;}
            .div2{ width:40px ; background-color: green;}

            .div11{
                display: table-cell;vertical-align: middle;
            }
            .div22{
                margin: auto;
            }
        </style>

        <div class="div1 div11">
            <div class="div2 div22">
               div居中方法
            </div>
        </div>

    </body>
</html>