居中方法整理

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1.水平居中

行内元素：对父元素设置text-align:center;
定宽块状元素: 设置左右margin值为auto;
不定宽块状元素: 设置子元素为display:inline,然后在父元素上设置text-align:center;
通用方案: flex布局，对父元素设置display:flex;justify-content:center;

2.垂直居中

父元素一定，子元素为单行内联文本：设置父元素的height等于行高line-height
父元素一定，子元素为多行内联文本：设置父元素的display:table-cell或inline-block，再设置vertical-align:middle;
块状元素:设置子元素position:absolute 并设置top、bottom为0，父元素要设置定位为static以外的值，margin:auto;

通用方案: flex布局，给父元素设置{display:flex; align-items:center;}

3.左右布局

使盒子浮动，或者使用绝对定位等方法
浮动布局
这种方法是左边浮动，右边加上一个margin-left值，让他实现左边固定，右边自适应的布局效果
image.png

4.上中下布局

1. float+margin

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<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style type="text/css">
        #content{
            height:300px;
        }
        .left{
            width: 200px;
            height:100%;
            float: left;
            background-color: #00a0dc;
        }
        .middle{
            height:100%;
            margin-left:200px;
            margin-right: 300px;
            background-color: red;
        }
        .right{
            height:100%;
            width: 300px;
            float: right;
            background-color: #00a0dc;
        }
    </style>
</head>
<body>
<div id="content">
    <div class="left"></div>
    <div class="right"></div>
    <div class="middle"></div>
</div>
</body>
</html>

注意：中间的middle元素是content的最后一个元素

2. float+absolute

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<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style type="text/css">
        #content{
            position: relative;
            width:100%;
            height:300px;
        }
        .left{
            float: left;
            width: 200px;
            height:100%;
            background-color: #00a0dc;
        }
        .middle{
            position: absolute;
            top:0;
            bottom:0;
            left:200px;
            right: 300px;
            background-color: red;
        }
        .right{
            float: right;
            height:100%;
            width: 300px;
            background-color: #00a0dc;
        }
    </style>
</head>
<body>
<div id="content">
    <div class="left"></div>
    <div class="middle"></div>
    <div class="right"></div>
</div>
</body>
</html>

3. display:box;box-flex:1

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<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style type="text/css">
        #content{
            height:300px;
            display:-webkit-box;
        }
        .left{
            width: 200px;
            height:100%;
            background-color: #00a0dc;
        }
        .middle{
            min-width:200px;
            -webkit-box-flex: 1;
            height:100%;
            background-color: red;
        }
        .right{
            height:100%;
            width: 300px;
            background-color: #00a0dc;
        }
    </style>
</head>
<body>
<div id="content">
    <div class="left"></div>
    <div class="middle"></div>
    <div class="right"></div>
</div>
</body>
</html>

4. display:flex;flex:1

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<!DOCTYPE html>
<html>

<head>
    <meta charset="UTF-8">
    <title></title>
    <style type="text/css">
        *{
            margin: 0;
            padding: 0;
        }
        #content {
            display: flex;
            width: 100%;
            height: 200px;
        }
        #left {
           flex:0 0 200px;
            height: 100%;
            background-color: #f04d0d;
        }
        #middle{
            flex: 1;
            background-color: blue;
        }
        #right {
            flex:0 0 200px;
            height: 100%;
            background-color: #f04d0d;
        }
    </style>
</head>

<body>
<div id="content">
    <div id="left"> </div>
    <div id="middle"></div>
    <div id="right"></div>
</div>
</body>
</html>