如何实现CSS居中？–CSS居中常用方法

来源：http://www.ido321.com/824.html

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: }