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