文章參考：http://css-tricks.com/centering-css-complete-guide/?utm_source=ourjs.com（翻譯不當之處請諒解）
一、水平居中
1、內聯元素居中：相對父級塊級元素居中對齊
1: .center-children {
2: text-align: center;
3: }
2、塊級元素居中：設定margin-left和margin-right為auto讓它居中（同時還要設定width，否則它就會承滿整個容器，無法看出居中效果）
1: .center-me {
2: margin: 0 auto;
3: }
如果有很多塊級元素需要水平居中成一行，最好使用一個不同的display型別。這是一個使用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、內聯元素：設定相等的上下padding，或者利用line-height
1: .link {
2: padding-top: 30px;
3: padding-bottom: 30px;
4: }
文字不會換行的情況下，可以使用line-height，讓其與height相等去對齊文字。
1: .center-text-trick {
2: height: 100px;
3: line-height: 100px;
4: white-space: nowrap;
5: }
多行的文字也可以利用上下等padding的方式也可以讓多行居中，但是如果這方法沒用，你可以讓這些文字的容器按table cell模式顯示，然後設定文字的vertical-align屬性對齊，
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、塊級元素
若元素有固定高度，可以這樣垂直居中
1: .parent {
2: position: relative;
3: }
4: .child {
5: position: absolute;
6: top: 50%;
7: height: 100px;
8: margin-top: -50px; /* 如果沒有使用: border-box; 的盒子模型則需要設定這個 */
9: }
如果不知道元素高度，則這樣
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、同時水平和垂直居中
1、元素有固定高度和寬度：先絕對居中，然後上移和左移50%的寬度即可
1: //這種方案有極好的跨瀏覽器支援。
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、元素的高度和寬度未知或可變的：使用transofrm屬性在兩個方向都平移負50%
1: .parent {
2: position: relative;
3: }
4: .child {
5: position: absolute;
6: top: 50%;
7: left: 50%;
8: transform: translate(-50%, -50%);
9: }