# 1、定宽高

## 一、绝对定位和负magin值

``````<template>
<div id="app">
<div class="box">
<div class="children-box"></div>
</div>
</div>
</template>
<style type="text/css">
.box {
width: 200px;
height: 200px;
border: 1px solid red;
position: relative;
}
.children-box {
position: absolute;
width: 100px;
height: 100px;
background: yellow;
left: 50%;
top: 50%;
margin-left: -50px;
margin-top: -50px;
}
</style>

## 二、绝对定位 + transform

``````<template>
<div id="app">
<div class="box">
<div class="children-box"></div>
</div>
</div>
</template>
<style type="text/css">
.box {
width: 200px;
height: 200px;
border: 1px solid red;
position: relative;
}
.children-box {
position: absolute;
width: 100px;
height: 100px;
background: yellow;
left: 50%;
top: 50%;
transform: translate(-50%, -50%);
}
</style>

## 三、绝对定位 + left/right/bottom/top + margin

``````<template>
<div id="app">
<div class="box">
<div class="children-box"></div>
</div>
</div>
</template>
<style type="text/css">
.box {
width: 200px;
height: 200px;
border: 1px solid red;
position: relative;
}
.children-box {
position: absolute;
display: inline;
top: 0;
left: 0;
right: 0;
bottom: 0px;
background: yellow;
margin: auto;
height: 100px;
width: 100px;
}
</style>

## 四、flex布局

``````<template>
<div id="app">
<div class="box">
<div class="children-box"></div>
</div>
</div>
</template>
<style type="text/css">
.box {
width: 200px;
height: 200px;
border: 1px solid red;
display: flex;
justify-content: center;
align-items: center;
}
.children-box {
background: yellow;
height: 100px;
width: 100px;
}
</style>

## 五、grid布局

``````<template>
<div id="app">
<div class="box">
<div class="children-box"></div>
</div>
</div>
</template>
<style type="text/css">
.box {
width: 200px;
height: 200px;
border: 1px solid red;
display: grid;
}
.children-box {
width: 100px;
height: 100px;
background: yellow;
margin: auto;
}
</style>

## 六、table-cell + vertical-align + inline-block/margin: auto

``````<template>
<div id="app">
<div class="box">
<div class="children-box"></div>
</div>
</div>
</template>
<style type="text/css">
.box {
width: 200px;
height: 200px;
border: 1px solid red;
display: table-cell;
text-align: center;
vertical-align: middle;
}
.children-box {
width: 100px;
height: 100px;
background: yellow;
display: inline-block;// 可以换成margin: auto;
}
</style>

# 2、不定宽高

## 一、绝对定位 + transform

``````<template>
<div id="app">
<div class="box">
<div class="children-box">111111</div>
</div>
</div>
</template>
<style type="text/css">
.box {
width: 200px;
height: 200px;
border: 1px solid red;
position: relative;
}
.children-box {
position: absolute;
background: yellow;
left: 50%;
top: 50%;
transform: translate(-50%, -50%);
}
</style>

## 二、table-cell

``````<template>
<div id="app">
<div class="box">
<div class="children-box">111111</div>
</div>
</div>
</template>
<style type="text/css">
.box {
width: 200px;
height: 200px;
border: 1px solid red;
display: table-cell;
text-align: center;
vertical-align: middle;
}
.children-box {
background: yellow;
display: inline-block;
}
</style>

## 三、flex布局

``````<template>
<div id="app">
<div class="box">
<div class="children-box">11111111</div>
</div>
</div>
</template>
<style type="text/css">
.box {
width: 200px;
height: 200px;
border: 1px solid red;
display: flex;
justify-content: center;
align-items: center;
}
.children-box {
background: yellow;
}
</style>

## 四、flex变异布局

``````<template>
<div id="app">
<div class="box">
<div class="children-box">11111111</div>
</div>
</div>
</template>
<style type="text/css">
.box {
width: 200px;
height: 200px;
border: 1px solid red;
display: flex;
}
.children-box {
background: yellow;
margin: auto;
}
</style>

## 五、grid + flex布局

``````<template>
<div id="app">
<div class="box">
<div class="children-box">11111111</div>
</div>
</div>
</template>
<style type="text/css">
.box {
width: 200px;
height: 200px;
border: 1px solid red;
display: grid;
}
.children-box {
background: yellow;
align-self: center;
justify-self: center;
}
</style>

## 六、gird + margin布局

``````<template>
<div id="app">
<div class="box">
<div class="children-box">11111111</div>
</div>
</div>
</template>
<style type="text/css">
.box {
width: 200px;
height: 200px;
border: 1px solid red;
display: grid;
}
.children-box {
background: yellow;
margin: auto;
}
</style>

## 七、writing-mode属性布局

``````<template>
<div id="app">
<div class="box">
<div class="children-box">
<p>11111</p>
</div>
</div>
</div>
</template>
<style type="text/css">
.box {
width: 200px;
height: 200px;
border: 1px solid red;
writing-mode: vertical-lr;
text-align: center;
}

.box>.children-box {
writing-mode: horizontal-tb;
display: inline-block;
text-align: center;
width: 100%;
}

.box>.children-box>p {
display: inline-block;
margin: auto;
text-align: left;
background: yellow;
}
</style>

writing-mode 属性定义了文本在水平或垂直方向上如何排布。 兼容性上还有些小瑕疵，但大部分浏览器已经支持。

# 3、番外(图片定高|不定高水平垂直居中)

## 一、table-cell

``````<template>
<div id="app">
<div class="box">
<img src="https://ss1.baidu.com/70cFfyinKgQFm2e88IuM_a/forum/pic/item/242dd42a2834349b406751a3ceea15ce36d3beb6.jpg">
</div>
</div>
</template>
<style type="text/css">
.box {
height: 200px;
width: 200px;
display: table-cell;
text-align: center;
border: 1px solid #ccc;
vertical-align: middle;
}
</style>

## 二、 ::after

``````<template>
<div id="app">
<div class="box">
<img src="https://ss1.baidu.com/70cFfyinKgQFm2e88IuM_a/forum/pic/item/242dd42a2834349b406751a3ceea15ce36d3beb6.jpg">
</div>
</div>
</template>
<style type="text/css">
.box {
width: 200px;
height: 200px;
border: 1px solid red;
text-align: center;
}

.box::after {
content: '';
display: inline-block;
vertical-align: middle;
height: 100%;
}
img {
vertical-align: middle;
}
</style>

## 三、 ::before

``````<template>
<div id="app">
<div class="box">
<img src="https://ss1.baidu.com/70cFfyinKgQFm2e88IuM_a/forum/pic/item/242dd42a2834349b406751a3ceea15ce36d3beb6.jpg">
</div>
</div>
</template>
<style type="text/css">
.box {
width: 200px;
height: 200px;
border: 1px solid #ccc;

text-align: center;
font-size: 0;
}

.box::before {
display: inline-block;
vertical-align: middle;
content: '';
height: 100%;
}

img {
vertical-align: middle;
}
</style>

# 四、总结

## 一、内联元素居中布局

1. 水平居中
• 行内元素可设置：text-align: center;
• flex布局设置父元素：display: flex; justify-content: center;
1. 垂直居中
• 单行文本父元素确认高度：height === line-height
• 多行文本父元素确认高度：disaply: table-cell; vertical-align: middle;

## 二、块级元素居中布局

1. 水平居中
• 定宽: margin: 0 auto;
• 不定宽： 参考上诉例子中不定宽高例子。
1. 垂直居中
• position: absolute设置left、top、margin-left、margin-to(定高)；
• position: fixed设置margin: auto(定高)；
• display: table-cell；
• transform: translate(x, y)；
• flex(不定高，不定宽)；
• grid(不定高，不定宽)，兼容性相对比较差；