居中总结

居中：盒子在其包含快中居中

行盒（行块盒）居中

直接设置行盒（块）父元素 text-align:center

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div{
            background-color: lightblue;
            height: 100px;
            text-align: center;
        }

        .inline-block{
            display: inline-block;
            width: 300px;
            height: 50px;
            background-color: red;
        }
    </style>
</head>
<body>
    <div>
        <a href="">超链接</a>
    </div>

    <div>
        <span class="inline-block"></span>
    </div>

    <div>
        <img src="" alt="">
    </div>
    <div>
        <input type="text">
    </div>
</body>
</html>

常规流块盒的水平居中

定宽，设置左右margin为auto
一定要定宽，否则宽度为auto，会撑满，吸收能力大于margin

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .container{
            margin: 30px;
            height: 500px;
            background-color: lightblue;
        }

        p{
            width: 500px;
            height: 100px;
            background-color: red;
            margin: 0 auto;
        }
    </style>
</head>
<body>
    <div class="container">
        <p></p>
    </div>
</body>
</html>

绝对定位元素的水平居中

定宽，设置左右坐标为0（left:0 right:0）将margin设置为auto

实际上固定定位fixed(包含快是视口)是绝对定位absolute(父元素填充盒是包含快)的特殊情况

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .container{
            margin: 30px;
            height: 200px;
            background-color: lightblue;
            position: relative;
        }

        p{
            width: 500px;
            height: 100px;
            background-color: red;
            left: 0;
            right: 0;
            margin: 0 auto;
            /* 父元素的填充盒为其包含快 */
            position: absolute;
        }
    </style>
</head>
<body>
    <div class="container">
        <p></p>
    </div>
</body>
</html>

单行文本的垂直居中

设置文本所在元素的行高，为整个区域的高度

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        h1{
            background-color: lightblue;
            height: 200px;
            text-align: center;
            line-height: 200px;
        }
    </style>
</head>
<body>
    <h1>
        biaoti
    </h1>
</body>
</html>

行块盒或块盒内多行文本垂直居中

没有完美方案，
设置盒子上下内边距相同，达到类似效果

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div{
            background-color: lightblue;
            display: inline-block;
            padding: 100px 0;
        }
    </style>
</head>
<body>
    <div>
        Lorem ipsum dolor sit amet consectetur adipisicing elit. Illum possimus corporis eveniet voluptas! Corporis placeat iusto temporibus reiciendis illum ex impedit, expedita recusandae ea veritatis iure debitis quo et modi?
    </div>
</body>
</html>