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方法1:宽度和高度已知的。
思路:
给父元素相对定位
给子元素绝对定位
left: 50%;top: 50%;
margin-left: 负的宽度一半。
margin-top: 负的高度一半;
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>居中</title>
<style type="text/css">
#box{
width: 400px;
height: 200px;
position: relative;
background: red;
}
#box1{
width: 200px;
height: 100px;
position: absolute;
top: 50%;
left: 50%;
margin-left: -100px;
margin-top: -50px;
background: green;
}
</style>
</head>
<body>
<div id="box">
<div id="box1">
</div>
</div>
</body>
</html>
方法2:宽度和高度自己未知
意思就是说子盒子本身还是有宽度和高度的,只是自己未知。
思路:
给父盒子相对定位
给子盒子绝对定位
top、right、bottom、left全为0
margin: auto;
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>居中</title>
<style type="text/css">
#box{
width: 800px;
height: 400px;
position: relative;
background: red;
}
#box1{
width: 100px;
height: 50px;
position: absolute;
top: 0;
right: 0;
bottom: 0;
left: 0;
margin: auto;
background: green;
}
</style>
</head>
<body>
<div id="box">
<div id="box1">
</div>
</div>
<script type="text/javascript">
</script>
</body>
</html>
方法3:flex布局
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>垂直居中</title>
<style type="text/css">
.box{
width: 400px;
height: 200px;
background: #f99;
}
.box1{
width: 200px;
height: 100px;
background: green;
}
.center{
display: flex;
justify-content: center;//实现水平居中
align-items: center;//实现垂直居中
}
</style>
</head>
<body>
<div class="box center">
<div class="box1">
</div>
</div>
</body>
</html>
方法四:平移 定位+transform
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>css3让一个盒子居中</title>
<style type="text/css">
.parent_box{
width: 400px;
height: 200px;
background: red;
position: relative;
}
.child_box{
width: 200px;
height: 100px;
background: #9ff;
position: absolute;
top: 50%;
left: 50%;
transform: translate( -50%,-50%);
}
</style>
</head>
<body>
<div class="parent_box">
<div class="child_box">
</div>
</div>
</body>
</html>
方法五:table-cell布局
父级 display: table-cell; vertical-align: middle; 子级 margin: 0 auto;
**水平方向的居中
再加一种水平方向上居中 :margin-left : 50% ; transform: translateX(-50%);