CSS3/CSS之居中解析（水平+垂直居中、水平居中，垂直居中）

首先，我们来看下垂直居中：

（1）、如果是单行文本，则可以设置的line-height的数值，让其等于父级元素的高度！

<!DOCTYPE html>

<html lang="en">

<head>

    <meta charset="UTF-8">

    <meta name="viewport" content="width=device-width, initial-scale=1.0">

    <meta http-equiv="X-UA-Compatible" content="ie=edge">

    <title>Document</title>

    <style>

        .box{

            background: green;

            height:200px;

        }

        a {height:%;

        line-height: 200px;

        color:red;

}

 </style>

</head>

<body>

   <div class="box">

       <a href="">ggg </a>

   </div>

</body>

</html>

（2）、如果元素是行内块级元素，一般会使用diaplay:inline-block,vertical-align:middle，还有一个伪元素让元素内容处于容器中央！给父元素添加伪元素！

<!DOCTYPE html>

<html lang="en">

<head>

    <meta charset="UTF-8">

    <meta name="viewport" content="width=device-width, initial-scale=1.0">

    <meta http-equiv="X-UA-Compatible" content="ie=edge">

    <title>Document</title>

    <style>

        .box {

            background: green;

            height:200px;

        }

     .box::after, .box2{

         display:inline-block;

         vertical-align: middle;

     }

     .box::after{

         content:'';

         height:%;

     }

     .box2{background-color:red;width:20px;height:20px;}

 </style>

</head>

<body>

   <div class="box">

       <div class="box2"></div>

   </div>

</body>

</html>

（3）、通过display：flex来实现垂直居中；

父级：display：flex；

子元素：align-self：center；

<!DOCTYPE html>

<html lang="en">

<head>

    <meta charset="UTF-8">

    <meta name="viewport" content="width=device-width, initial-scale=1.0">

    <meta http-equiv="X-UA-Compatible" content="ie=edge">

    <title>Document</title>

    <style>

        .box {

            background: green;

            height:300px;

            width: 600px;

            display:flex;

        }

        .box2{background:red;

        width:%;

        height:%;

        align-self: center;

     }

 </style>

</head>

<body>

   <div class="box">

       <div class="box2"></div>

   </div>

</body>

</html>

（4）、使用display：table进行垂直居中！

给父元素设置display：table；子元素设置为display：table-cell;

<!DOCTYPE html>

<html lang="en">

<head>

    <meta charset="UTF-8">

    <meta name="viewport" content="width=device-width, initial-scale=1.0">

    <meta http-equiv="X-UA-Compatible" content="ie=edge">

    <title>Document</title>

    <style>

        .box {

            background-color: green;

            height:300px;

            width: 600px;

            display:table;

        }

       .box .box2{

           color:red;

        display:table-cell;

         vertical-align: middle;

}

 </style>

</head>

<body>

   <div class="box">

       <div class="box2">ddddd</div>

   </div>

</body>

</html>

（5），已经知道父元素的高度，给子元素相对定位，在通过translaY（）得到垂直居中

<!DOCTYPE html>

<html lang="en">

<head>

    <meta charset="UTF-8">

    <meta name="viewport" content="width=device-width, initial-scale=1.0">

    <meta http-equiv="X-UA-Compatible" content="ie=edge">

    <title>Document</title>

    <style>

        .box {

            background-color: green;

            height:300px;

            width: 600px;

        }

       .box .box2{

           background-color:red;

            width:%;

             height:%;

             position: relative;

             top:%;

             transform:translateY(-%);

}

 </style>

</head>

<body>

   <div class="box">

       <div class="box2"></div>

   </div>

</body>

</html>

6)、父元素高度不知道，同过transform实现，先给父元素相对定位，在给子元素绝对定位

<!DOCTYPE html>

<html lang="en">

<head>

    <meta charset="UTF-8">

    <meta name="viewport" content="width=device-width, initial-scale=1.0">

    <meta http-equiv="X-UA-Compatible" content="ie=edge">

    <title>Document</title>

    <style>

        .box {

            background-color: green;

            height:300px;

            width: 600px;

            position: relative;

        }

       .box .box2{

           background-color:red;

            width:%;

             height:%;

             position: absolute;

             top:%;

             transform:translateY(-%);

}

 </style>

</head>

<body>

   <div class="box">

       <div class="box2"></div>

   </div>

</body>

</html>

二、水平居中：

（1）、行内元素方案，只要把行内元素包裹在一个盒子中，并且在他父级元素添加如下属性：text-align：center；

<!DOCTYPE html>

<html lang="en">

<head>

    <meta charset="UTF-8">

    <meta name="viewport" content="width=device-width, initial-scale=1.0">

    <meta http-equiv="X-UA-Compatible" content="ie=edge">

    <title>Document</title>

    <style>

        .box {

            background-color: green;

            height:300px;

            width: 600px;

            text-align:center;

        }

      P{color:red;}

 </style>

</head>

<body>

   <div class="box">

       <p>1111</p>

   </div>

</body>

</html>

（2）、单个块状元素解决方案：

<!DOCTYPE html>

<html lang="en">

<head>

    <meta charset="UTF-8">

    <meta name="viewport" content="width=device-width, initial-scale=1.0">

    <meta http-equiv="X-UA-Compatible" content="ie=edge">

    <title>Document</title>

    <style>

        .box {

            background-color: green;

            height:300px;

            width: 600px;

            text-align:center;

        }

    .box2{

        background-color: red;

        width: 20px;

        height: 20px;

        margin: auto;

    }

 </style>

</head>

<body>

   <div class="box">

       <div class="box2"></div>

   </div>

</body>

</html>

3）、多个块状元素解决方案：父元素设置为text-align：center；子元素设置为：display：inline-block;

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!DOCTYPE html>

<html lang="en">

<head>

    <meta charset="UTF-8">

    <meta name="viewport" content="width=device-width, initial-scale=1.0">

    <meta http-equiv="X-UA-Compatible" content="ie=edge">

    <title>Document</title>

    <style>

        .box {

            background-color: green;

            height:300px;

            width: 600px;

            text-align:center;

        }

    .box2, .box3{

        background-color: red;

        width: 20px;

        height: 20px;

        display:inline-block;

    }

 </style>

</head>

<body>

   <div class="box">

       <div class="box2"></div>

       <div class="box3"></div>

   </div>

</body>

</html>

也可以使用flexbox来实现：

<!DOCTYPE html>

<html lang="en">

<head>

    <meta charset="UTF-8">

    <meta name="viewport" content="width=device-width, initial-scale=1.0">

    <meta http-equiv="X-UA-Compatible" content="ie=edge">

    <title>Document</title>

    <style>

        .box {

            background-color: green;

            height:300px;

            width: 600px;

           display:flex;

           justify-content:center;

        }

    .box2, .box3, .box4{

        background-color: red;

        width: 20px;

        height: 20px;

    }

 </style>

</head>

<body>

   <div class="box">

       <div class="box2"></div>

       <div class="box3"></div>

       <div class="box4"></div>

   </div>

</body>

</html>

（4）、不定宽度块元素水平居中：

<!DOCTYPE html>

<html lang="en">

<head>

    <meta charset="UTF-8">

    <meta name="viewport" content="width=device-width, initial-scale=1.0">

    <meta http-equiv="X-UA-Compatible" content="ie=edge">

    <title>Document</title>

    <style>

        .box {

            float:left;

            position: relative;

            left:%;

        }

    .box ul{

        position:relative;

        left:-%;

    }

 </style>

</head>

<body>

   <div class="box">

       <ul>

           <li></li>

           <li></li>

           <li></li>

       </ul>

   </div>

</body>

</html>

三：实现水平+垂直居中，也就是在中央：（1）单行行内元素：父元素设置：text-align:center，display：table-cell;vertical-align:middle,在这里，图片，文字，都是一样的操作

<!DOCTYPE html>

<html lang="en">

<head>

    <meta charset="UTF-8">

    <meta name="viewport" content="width=device-width, initial-scale=1.0">

    <meta http-equiv="X-UA-Compatible" content="ie=edge">

    <title>Document</title>

    <style>

        .box {

            background-color: #ccc;

            width:500px;

            height: 500px;

            display:table-cell;

            text-align: center;

            vertical-align: middle;

        }

        img{width:50px;

        height: 50px;}

 </style>

</head>

<body>

   <div class="box">

      <img src="5.jpg" alt="">

   </div>

</body>

</html>

文字在中央，还可以父级设置为text-align:center;line-height设置为父元素的height

<!DOCTYPE html>

<html lang="en">

<head>

    <meta charset="UTF-8">

    <meta name="viewport" content="width=device-width, initial-scale=1.0">

    <meta http-equiv="X-UA-Compatible" content="ie=edge">

    <title>Document</title>

    <style>

        .box {

            background-color: #ccc;

            width:500px;

            height: 500px;

            text-align: center;

        }

   p{line-height: 500px;}

 </style>

</head>

<body>

   <div class="box">

  <p></p>

   </div>

</body>

（2）对于单个块级元素，父元素设置为相对定位，子元素设置为绝对定位高度，宽度为50%

!DOCTYPE html>

<html lang="en">

<head>

    <meta charset="UTF-8">

    <meta name="viewport" content="width=device-width, initial-scale=1.0">

    <meta http-equiv="X-UA-Compatible" content="ie=edge">

    <title>Document</title>

    <style>

        .box {

            background-color: #ccc;

            width:500px;

            height: 500px;

            position: relative;

        }

        .box2{position: absolute;

        top:%;

        left:%;

        background-color: black;

        width: 20px;

        height: 20px;}

 </style>

</head>

<body>

   <div class="box">

       <div class="box2"></div>

   </div>

</body>

</html>

（3）、flex实现不定宽度水平+垂直居中

<!DOCTYPE html>

<html lang="en">

<head>

    <meta charset="UTF-8">

    <meta name="viewport" content="width=device-width, initial-scale=1.0">

    <meta http-equiv="X-UA-Compatible" content="ie=edge">

    <title>Document</title>

    <style>

        .box {

            background-color: green;

            height:300px;

            width: 600px;

           display:flex;

           justify-content:center;

           align-items:center;

        }

    .box2, .box3, .box4{

        background-color: red;

        width: 20px;

        height: 20px;

    }

 </style>

</head>

<body>

   <div class="box">

       <div class="box2"></div>

   </div>

</body>

</html>

巴特西

CSS3/CSS之居中解析（水平+垂直居中、水平居中，垂直居中）

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