本文翻譯自 CSS Tricks 中關於居中的相關介紹。
1、水平居中
1.1 內聯元素的水平居中(如鏈接或文本)
可以在一個塊級別的父元素中水平地居中內聯元素,只需:
.center-children {
text-align: center;
}
注:這種寫法適用於inline, inline-block, inline-table, inline-flex等等。
代碼示例:
=> html代碼
<header>
This text is centered.
</header>
<nav role='navigation'>
<a href="#0">One</a>
<a href="#0">Two</a>
<a href="#0">Three</a>
<a href="#0">Four</a>
</nav>
=> css代碼
body {
background: #f06d06;
}
header, nav {
text-align: center;
background: white;
margin: 20px 0;
padding: 10px;
}
nav a {
text-decoration: none;
background: #333;
border-radius: 5px;
color: white;
padding: 3px 8px;
}
=> 效果圖
1.2 塊級元素水平居中
可以通過給它設置margin-left
和margin-right
爲auto
(並且該元素需有width
屬性,否則它將佔滿整行,無法居中)來居中一個塊級元素。通常用這樣的速記法來做:
.center-me {
margin: 0 auto;
}
注:無論您所處的塊級別元素的寬度是多少,還是父節點,這都是可行的。
注意:你不能浮動一個元素到水平居中的位置 ,不過有一個小技巧(本文不再詳述,可點擊鏈接自行查看)。
代碼示例:
=> html代碼
<main>
<div class="center">
I'm a block level element and am centered.
</div>
</main>
=> css代碼
body {
background: #f06d06;
}
main {
background: white;
margin: 20px 0;
padding: 10px;
}
.center {
margin: 0 auto;
width: 200px;
background: black;
padding: 20px;
color: white;
}
=> 效果圖
1.3 兩個及以上的多個塊級元素水平居中
如果您有兩個或多個塊級別的元素,它們需要在一行中水平居中,那麼最好將它們作爲不同的display
。比如設置其爲display:inline-block
。
代碼示例1:
注:下面的示例中,inline-block-center的<main>
標籤中,是把父元素設置text-align:center
,子元素設置display:inline-block
;
flex-center的<main>
標籤中,使用了CSS3中新增的彈性盒子(附帶MDN相關介紹)是把父元素設置display: flex;justify-content: center;
=>html代碼
<main class="inline-block-center">
<div>
I'm an element that is block-like with my siblings and we're centered in a row.
</div>
<div>
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.
</div>
<div>
I'm an element that is block-like with my siblings and we're centered in a row.
</div>
</main>
<main class="flex-center">
<div>
I'm an element that is block-like with my siblings and we're centered in a row.
</div>
<div>
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.
</div>
<div>
I'm an element that is block-like with my siblings and we're centered in a row.
</div>
</main>
=>css代碼
body {
background: #f06d06;
font-size: 80%;
}
main {
background: white;
margin: 20px 0;
padding: 10px;
}
main div {
background: black;
color: white;
padding: 15px;
max-width: 125px;
margin: 5px;
}
.inline-block-center {
text-align: center;
}
.inline-block-center div {
display: inline-block;
text-align: left;
}
.flex-center {
display: flex;
justify-content: center;
}
=>效果圖
代碼示例2:
注:下面的例子中,表現的是你有多個塊級元素堆疊在一起,在這種情況下,自動邊距(即margin:0 auto
)仍然很好。即多個塊級元素不需要在一行顯示,居中的方法仍使用margin:0 auto
。
=>html代碼
<main>
<div>
I'm an element that is block-like with my siblings and we're centered in a row.
</div>
<div>
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.
</div>
<div>
I'm an element that is block-like with my siblings and we're centered in a row.
</div>
</main>
=>css代碼
body {
background: #f06d06;
font-size: 80%;
}
main {
background: white;
margin: 20px 0;
padding: 10px;
}
main div {
background: black;
margin: 0 auto;
color: white;
padding: 15px;
margin: 5px auto;
}
main div:nth-child(1) {
width: 200px;
}
main div:nth-child(2) {
width: 400px;
}
main div:nth-child(3) {
width: 125px;
}
=>效果圖
2、垂直居中
2.1 內聯元素垂直居中
2.1.1 單行內聯元素垂直居中
代碼示例1:
單行內聯元素使用上下相同的padding造成垂直居中的效果
.link {
padding-top: 30px;
padding-bottom: 30px;
}
=>效果圖
代碼示例2:
當某些情況下,不適合使用padding填充時,可以讓其文本的行高=父元素的高度達到垂直居中的效果。
=>html代碼
<main>
<div>
I'm a centered line.
</div>
</main>
=>css代碼
body {
background: #f06d06;
font-size: 80%;
}
main {
background: white;
margin: 20px 0;
padding: 40px;
}
main div {
background: black;
color: white;
height: 100px;
line-height: 100px;
padding: 20px;
width: 50%;
white-space: nowrap;
}
=>效果圖
2.1.2 多行內聯元素垂直居中
代碼示例1:
使用表格佈局居中(基本過時的用法)
注:下面的例子中,第一個效果圖展示的是直接使用<table>
標籤(其<td>
標籤默認垂直居中),第二個效果圖展示的是父元素<div>
設置display:table
,子元素<p>
設置display: table-cell;vertical-align: middle;
=>html代碼
<table>
<tr>
<td>
I'm vertically centered multiple lines of text in a real table cell.
</td>
</tr>
</table>
<div class="center-table">
<p>I'm vertically centered multiple lines of text in a CSS-created table layout.</p>
</div>
=>css代碼
body {
background: #f06d06;
font-size: 80%;
}
table {
background: white;
width: 240px;
border-collapse: separate;
margin: 20px;
height: 250px;
}
table td {
background: black;
color: white;
padding: 20px;
border: 10px solid white;
/* default is vertical-align: middle; */
}
.center-table {
display: table;
height: 250px;
background: white;
width: 240px;
margin: 20px;
}
.center-table p {
display: table-cell;
margin: 0;
background: black;
color: white;
padding: 20px;
border: 10px solid white;
vertical-align: middle;
}
=>效果圖
代碼示例2:
使用flexbox來垂直居中。
精簡CSS代碼如下:
.flex-center-vertically {
display: flex;
justify-content: center;
flex-direction: column;
height: 400px;
}
具體示例:
=>html代碼
<div class="flex-center">
<p>I'm vertically centered multiple lines of text in a flexbox container.</p>
</div>
=>css代碼
body {
background: #f06d06;
font-size: 80%;
}
div {
background: white;
width: 240px;
margin: 20px;
}
.flex-center {
background: black;
color: white;
border: 10px solid white;
display: flex;
flex-direction: column;
justify-content: center;
height: 200px;
resize: vertical;
overflow: auto;
}
.flex-center p {
margin: 0;
padding: 20px;
}
=>效果圖
代碼示例3:
使用僞元素來垂直居中。
精簡CSS代碼如下:
.ghost-center {
position: relative;
}
.ghost-center::before {
content: " ";
display: inline-block;
height: 100%;
width: 1%;
vertical-align: middle;
}
.ghost-center p {
display: inline-block;
vertical-align: middle;
}
=>html代碼
<div class="ghost-center">
<p>I'm vertically centered multiple lines of text in a container. Centered with a ghost pseudo element</p>
</div>
=>css代碼
body {
background: #f06d06;
font-size: 80%;
}
div {
background: white;
width: 240px;
height: 200px;
margin: 20px;
color: white;
resize: vertical;
overflow: auto;
padding: 20px;
}
.ghost-center {
position: relative;
}
.ghost-center::before {
content: " ";
display: inline-block;
height: 100%;
width: 1%;
vertical-align: middle;
}
.ghost-center p {
display: inline-block;
vertical-align: middle;
width: 190px;
margin: 0;
padding: 20px;
background: black;
}
=>效果圖
2.2 塊級元素垂直居中
不知道網頁佈局的高度是很常見的,原因有很多:如果寬度改變,文本流會改變高度。文本樣式的差異可以改變高度。文本數量的差異可以改變高度。具有固定寬寬比的元素,如圖像,可以在重置寬高時改變高度等等。
但是如果你已經知道高度,就可以這樣:
2.2.1 塊級元素的高度已知/確定
即設置子元素相對於父元素絕對定位,子元素設置top:50%
,並設置margin-top
爲負的子元素自身高度的一半。
.parent {
position: relative;
}
.child {
position: absolute;
top: 50%;
height: 100px;
margin-top: -50px; /* account for padding and border if not using box-sizing: border-box; */
}
代碼示例:
注:
=>html代碼
<main>
<div>
I'm a block-level element with a fixed height, centered vertically within my parent.
</div>
</main>
=>css代碼
body {
background: #f06d06;
font-size: 80%;
}
main {
background: white;
height: 300px;
margin: 20px;
width: 300px;
position: relative;
resize: vertical;
overflow: auto;
}
main div {
position: absolute;
top: 50%;
left: 20px;
right: 20px;
height: 100px;
margin-top: -70px;
background: black;
color: white;
padding: 20px;
}
=>效果圖
2.2.2 塊級元素的高度未知/不確定
它仍然可以通過將它的一半高度推到一半的高度來居中,即設置子元素transform: translateY(-50%);
,即:
.parent {
position: relative;
}
.child {
position: absolute;
top: 50%;
transform: translateY(-50%);
}
=>html代碼
<main>
<div>
I'm a block-level element with an unknown height, centered vertically within my parent.
</div>
</main>
=>css代碼
body {
background: #f06d06;
font-size: 80%;
}
main {
background: white;
height: 300px;
margin: 20px;
width: 300px;
position: relative;
resize: vertical;
overflow: auto;
}
main div {
position: absolute;
top: 50%;
left: 20px;
right: 20px;
background: black;
color: white;
padding: 20px;
transform: translateY(-50%);
resize: vertical;
overflow: auto;
}
=>效果圖
2.2.3 使用display:flex
佈局
即:
.parent {
display: flex;
flex-direction: column;
justify-content: center;
}
=>html代碼
<main>
<div>
I'm a block-level element with an unknown height, centered vertically within my parent.
</div>
</main>
=>css代碼
body {
background: #f06d06;
font-size: 80%;
}
main {
background: white;
height: 300px;
width: 200px;
padding: 20px;
margin: 20px;
display: flex;
flex-direction: column;
justify-content: center;
resize: vertical;
overflow: auto;
}
main div {
background: black;
color: white;
padding: 20px;
resize: vertical;
overflow: auto;
}
=>效果圖
3、水平居中+垂直居中
3.1 固定寬高的元素
使用負的margin
等於寬度和高度的一半,在你完全定位50%/50%之後,它會以巨大的跨瀏覽器支持爲中心,即:
.parent {
position: relative;
}
.child {
width: 300px;
height: 100px;
padding: 20px;
position: absolute;
top: 50%;
left: 50%;
margin: -70px 0 0 -170px;
}
代碼示例:
=>html代碼
<main>
<div>
I'm a block-level element a fixed height and width, centered vertically within my parent.
</div>
</main>
=>css代碼
body {
background: #f06d06;
font-size: 80%;
padding: 20px;
}
main {
position: relative;
background: white;
height: 200px;
width: 60%;
margin: 0 auto;
padding: 20px;
resize: both;
overflow: auto;
}
main div {
background: black;
color: white;
width: 200px;
height: 100px;
margin: -70px 0 0 -120px;
position: absolute;
top: 50%;
left: 50%;
padding: 20px;
}
=>效果圖
3.2 寬高未知的元素
如果你不知道寬度和高度,你可以使用transform屬性和在兩個方向上的負translate(它基於當前元素的寬度/高度)到中心,即:
.parent {
position: relative;
}
.child {
position: absolute;
top: 50%;
left: 50%;
transform: translate(-50%, -50%);
}
代碼示例:
=>html代碼
<main>
<div>
I'm a block-level element of an unknown height and width, centered vertically within my parent.
</div>
</main>
=>css代碼
body {
background: #f06d06;
font-size: 80%;
padding: 20px;
}
main {
position: relative;
background: white;
height: 200px;
width: 60%;
margin: 0 auto;
padding: 20px;
resize: both;
overflow: auto;
}
main div {
background: black;
color: white;
width: 50%;
transform: translate(-50%, -50%);
position: absolute;
top: 50%;
left: 50%;
padding: 20px;
resize: both;
overflow: auto;
}
=>效果圖
- #### 使用flexbox居中
要用flexbox向兩個方向居中,你需要使用兩個中心屬性,即:
.parent {
display: flex;
justify-content: center;
align-items: center;
}
=>html代碼
<main>
<div>
I'm a block-level-ish element of an unknown width and height, centered vertically within my parent.
</div>
</main>
=>css代碼
body {
background: #f06d06;
font-size: 80%;
padding: 20px;
}
main {
background: white;
height: 200px;
width: 60%;
margin: 0 auto;
padding: 20px;
display: flex;
justify-content: center;
align-items: center;
resize: both;
overflow: auto;
}
main div {
background: black;
color: white;
width: 50%;
padding: 20px;
resize: both;
overflow: auto;
}
=>效果圖
3.3 使用grid居中
這只是一個非常有效的小技巧(由Lance Janssen上傳)
=>html代碼
<div class="wrapper">
<span> I'm centered!</span>
</div>
=>css代碼
.wrapper{
height:300px;
width:300px;
border:1px solid red;
display: grid;
}
span {
margin: auto;
}
=>效果圖