如何实现CSS居中？–CSS居中常用方法

文章参考：http://css-tricks.com/centering-css-complete-guide/?utm_source=ourjs.com（翻译不当之处请谅解）

一、水平居中

1、内联元素居中：相对父级块级元素居中对齐

   1: .center-children {

   2:   text-align: center;

   3: }

2、块级元素居中：设置margin-left和margin-right为auto让它居中（同时还要设置width，否则它就会承满整个容器，无法看出居中效果）

   1: .center-me {

   2:   margin: 0 auto;

   3: }

如果有很多块级元素需要水平居中成一行，最好使用一个不同的display类型。这是一个使用inline-block和flex的例子。

演示地址：http://jsfiddle.net/Web_Code/5fvrwwk1/embedded/result/

1: <main class="inline-block-center">

   2:   <div>

   3:     I'm an element that is block-like with my siblings and we're centered in a row.

   4:   </div>

   5:   <div>

   6:     I'm an element that is block-like with my siblings and we're centered in a row. I have more content in me than my siblings do.

   7:   </div>

   8:   <div>

   9:     I'm an element that is block-like with my siblings and we're centered in a row.

  10:   </div>

  11: </main>

  12: <main class="flex-center">

  13:   <div>

  14:     I'm an element that is block-like with my siblings and we're centered in a row.

  15:   </div>

  16:   <div>

  17:     I'm an element that is block-like with my siblings and we're centered in a row. I have more content in me than my siblings do.

  18:   </div>

  19:   <div>

  20:     I'm an element that is block-like with my siblings and we're centered in a row.

  21:   </div>

  22: </main>

css:

  1: body {

   2:   background: #f06d06;

   3:   font-size: 80%;

   4: }

   5: main {

   6:   background: white;

   7:   margin: 20px 0;

   8:   padding: 10px;

   9: }

  10: main div {

  11:   background: black;

  12:   color: white;

  13:   padding: 15px;

  14:   max-width: 125px;

  15:   margin: 5px;

  16: }

  17: .inline-block-center {

  18:   text-align: center;

  19: }

  20: .inline-block-center div {

  21:   display: inline-block;

  22:   text-align: left;

  23: }

  24: .flex-center {

  25:   display: flex;

  26:   justify-content: center;

  27: }

二、垂直居中

1、内联元素：设置相等的上下padding，或者利用line-height

   1: .link {

   2:   padding-top: 30px;

   3:   padding-bottom: 30px;

   4: }

文本不会换行的情况下，可以使用line-height，让其与height相等去对齐文本。

 1: .center-text-trick {

   2:   height: 100px;

   3:   line-height: 100px;

   4:   white-space: nowrap;

   5: }

多行的文本也可以利用上下等padding的方式也可以让多行居中，但是如果这方法没用，你可以让这些文字的容器按table cell模式显示，然后设置文字的vertical-align属性对齐，
演示地址：http://jsfiddle.net/Web_Code/5fvrwwk1/1/embedded/result/
html:

  1: <table>

   2:   <tr>

   3:     <td>

   4:       I'm vertically centered multiple lines of text in a real table cell.

   5:     </td>

   6:   </tr>

   7: </table>

   8: <div class="center-table">

   9:   <p>I'm vertically centered multiple lines of text in a CSS-created table layout.</p>

  10: </div>

css

  1: body {

   2:   background: #f06d06;

   3:   font-size: 80%;

   4: }

   5: table {

   6:   background: white;

   7:   width: 240px;

   8:   border-collapse: separate;

   9:   margin: 20px;

  10:   height: 250px;

  11: }

  12: table td {

  13:   background: black;

  14:   color: white;

  15:   padding: 20px;

  16:   border: 10px solid white;

  17:   /* default is vertical-align: middle; */

  18: }

  19: .center-table {

  20:   display: table;

  21:   height: 250px;

  22:   background: white;

  23:   width: 240px;

  24:   margin: 20px;

  25: }

  26: .center-table p {

  27:   display: table-cell;

  28:   margin: 0;

  29:   background: black;

  30:   color: white;

  31:   padding: 20px;

  32:   border: 10px solid white;

  33:   vertical-align: middle;

  34: }

2、块级元素

若元素有固定高度，可以这样垂直居中

 1: .parent {

   2:   position: relative;

   3: }

   4: .child {

   5:   position: absolute;

   6:   top: 50%;

   7:   height: 100px;

   8:   margin-top: -50px; /* 如果没有使用: border-box; 的盒子模型则需要设置这个 */

   9: }

如果不知道元素高度，则这样

 1: .parent {

   2:   position: relative;

   3: }

   4: .child {

   5:   position: absolute;

   6:   top: 50%;

   7:   transform: translateY(-50%);

   8: }

也可以使用flexbox

   1: <main>

   2:   <div>

   3:      I'm a block-level element with an unknown height, centered vertically within my parent.

   4:   </div>

   5: </main>

   1: body {

   2:   background: #f06d06;

   3:   font-size: 80%;

   4: }

   5: main {

   6:   background: white;

   7:   height: 300px;

   8:   width: 200px;

   9:   padding: 20px;

  10:   margin: 20px;

  11:   display: flex;

  12:   flex-direction: column;

  13:   justify-content: center;

  14:   resize: vertical;

  15:   overflow: auto;

  16: }

  17: main div {

  18:   background: black;

  19:   color: white;

  20:   padding: 20px;

  21:   resize: vertical;

  22:   overflow: auto;

  23: }

三、同时水平和垂直居中

1、元素有固定高度和宽度：先绝对居中，然后上移和左移50%的宽度即可

 1: //这种方案有极好的跨浏览器支持。

   2: .parent {

   3:   position: relative;

   4: }

   5: .child {

   6:   width: 300px;

   7:   height: 100px;

   8:   padding: 20px;

   9:   position: absolute;

  10:   top: 50%;

  11:   left: 50%;

  12:   margin: -70px 0 0 -170px;

  13: }

2、元素的高度和宽度未知或可变的：使用transofrm属性在两个方向都平移负50%

 1: .parent {

   2:   position: relative;

   3: }

   4: .child {

   5:   position: absolute;

   6:   top: 50%;

   7:   left: 50%;

   8:   transform: translate(-50%, -50%);

   9: }

原文首发：http://www.ido321.com/824.html