<!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>