水平居中
内部块级元素的宽度要小于容器(父元素)
限制条件:仅用于内联元素 display:inline 和 display: inline-block;
给容器添加样式
text-align:center
DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>Documenttitle>
<style>
.box {
margin: 30px 30px 0px 300px;
border: 1px solid gray;
text-align: center;
}
.item {
display: inline-block;
width: 400px;
background: yellow;
}
style>
head>
<body>
<div class="box">
<span>水平居中 -- display: inlinespan>
div>
<div class="box">
<div class="item">水平居中 -- display: inline-blockdiv>
div>
body>
html>
限制条件:仅用于块级元素 display:block;
给内部元素添加样式
margin: auto
DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>Documenttitle>
<style>
.box {
margin: 30px;
border: 1px solid gray;
}
.item {
margin: auto;
width: 300px;
background: yellow;
}
style>
head>
<body>
<div class="box">
<div class="item">水平居中 -- 块级元素 display:blockdiv>
div>
body>
html>
给容器添加样式
display: flex;
justify-content: center;
DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>Documenttitle>
<style>
.box {
margin: 30px 30px 0px 300px;
border: 1px solid gray;
display: flex;
justify-content: center;
}
.item {
width: 400px;
background: yellow;
}
style>
head>
<body>
<div class="box">
<span>水平居中 -- flex布局 display: inlinespan>
div>
<div class="box">
<div class="item">水平居中 -- flex布局 display: blockdiv>
div>
body>
html>
限制条件:浏览器需支持CSS3,比较老的浏览器不适用
给容器(父元素)添加样式
position: relative
给内部元素添加样式
position: absolute;
left: 50%;
transform: translate(-50%, 0);
DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>Documenttitle>
<style>
.box {
margin: 30px 30px 0px 300px;
border: 1px solid gray;
height: 50px;
position: relative;
}
.item {
background-color: yellow;
position: absolute;
left: 50%;
transform: translate(-50%, 0);
}
style>
head>
<body>
<div class="box">
<span class="item">水平居中 -- 子绝父相 + transformspan>
div>
body>
html>
限制条件:内部元素需限定宽度
给容器(父元素)添加样式
position: relative
给内部元素添加样式
position: absolute;
left: 0;
right: 0;
margin: auto;
DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>Documenttitle>
<style>
.box {
margin: 30px 30px 0px 300px;
border: 1px solid gray;
height: 50px;
position: relative;
}
.item {
background-color: yellow;
position: absolute;
left: 0;
right: 0;
margin: auto;
width: 300px;
}
style>
head>
<body>
<div class="box">
<span class="item">水平居中 -- 子绝父相 + 自动外边距span>
div>
body>
html>
限制条件:需知道内部元素的宽度(无法预知宽度的内联元素和未知宽度的块级元素都不适用)
给容器(父元素)添加样式
position: relative
给内部元素添加样式
position: absolute;
left:50%;
margin-left:-内部元素宽度的一半
DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>Documenttitle>
<style>
.box {
margin: 30px;
border: 1px solid gray;
height: 100px;
position: relative;
}
.item {
width: 400px;
background: yellow;
position: absolute;
left: 50%;
margin-left: -200px;
}
style>
head>
<body>
<div class="box">
<div class="item">水平居中 -- 绝对定位元素 position:absolutediv>
div>
body>
html>
垂直居中
内部块级元素的高度要小于容器(父元素)
限制条件:仅用于单行内联元素 display:inline 和 display: inline-block;
给容器添加样式
height: 100px;
line-height: 100px;
DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>Documenttitle>
<style>
.box {
margin: 30px;
border: 1px solid gray;
height: 100px;
line-height: 100px;
}
style>
head>
<body>
<div class="box">
<span class="item">垂直居中 -- 内联元素 display:inlinespan>
div>
body>
html>
给容器添加样式
display: flex;
align-items: center;
限制条件:浏览器需支持CSS3,比较老的浏览器不适用
给容器(父元素)添加样式
position: relative
给内部元素添加样式
position: absolute;
top: 50%;
transform: translate(0, -50%);
DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>Documenttitle>
<style>
.box {
margin: 30px;
border: 1px solid gray;
height: 100px;
position: relative;
}
.item {
position: absolute;
top: 50%;
transform: translate(0, -50%);
background-color: yellow;
}
style>
head>
<body>
<div class="box">
<div class="item">垂直居中 -- 子绝父相 transformdiv>
div>
body>
html>
限制条件:内部元素需限定高度
给容器(父元素)添加样式
position: relative
给内部元素添加样式
position: absolute;
top: 0;
bottom: 0;
margin: auto;
DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>Documenttitle>
<style>
.box {
margin: 30px;
border: 1px solid gray;
height: 100px;
position: relative;
}
.item {
position: absolute;
top: 0;
bottom: 0;
margin: auto;
background-color: yellow;
height: 50px;
}
style>
head>
<body>
<div class="box">
<span class="item">垂直居中 -- 子绝父相 + 自动外边距span>
div>
body>
html>
限制条件:需知道内部元素的高度
给容器(父元素)添加样式
position: relative
给内部元素添加样式
position: absolute;
top: 50%;
margin-top: -内部元素高度的一半;
DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>Documenttitle>
<style>
.box {
margin: 30px;
border: 1px solid gray;
height: 100px;
position: relative;
}
.item {
position: absolute;
top: 50%;
margin-top: -25px;
height: 50px;
background-color: yellow;
}
style>
head>
<body>
<div class="box">
<span class="item">垂直居中 -- 子绝父相 + 负外边距span>
div>
body>
html>
水平垂直居中
参考上文分别实现水平居中和垂直居中即可,常用方案如下:
给容器添加样式
display: flex;
justify-content: center;
align-items: center;
限制条件:浏览器需支持CSS3,比较老的浏览器不适用
给容器(父元素)添加样式
position: relative
给内部元素添加样式
position: absolute;
top: 50%;
left: 50%;
transform: translate(-50%, -50%);
给容器(父元素)添加样式
position: relative
给内部元素添加样式
position: absolute;
top: 0;
bottom: 0;
left: 0;
right: 0;
margin: auto;
限制条件:需知道内部元素的宽度和高度
给容器(父元素)添加样式
position: relative
给内部元素添加样式
position: absolute;
left:50%;
margin-left:-内部元素宽度的一半;
top: 50%;
margin-top: -内部元素高度的一半;
DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>Documenttitle>
<style>
.box {
margin: 30px 30px 0px 300px;
border: 1px solid gray;
height: 100px;
position: relative;
}
.item {
background-color: yellow;
position: absolute;
left: 50%;
margin-left: -150px;
top: 50%;
margin-top: -25px;
width: 300px;
height: 50px;
}
style>
head>
<body>
<div class="box">
<span class="item">水平垂直居中 -- 子绝父相 + 负外边距span>
div>
body>
html>