居中一个元素

在这份指南中你将了解到把一个盒子居中放置在另一个之中的方法。在伸缩盒子模型(flexbox)出现之前,要做到同时垂直与水平居中是很困难的,而现在利用盒子对齐属性(Box Alignment)就很直截了当了。

an element centered inside a larger box

需求

把一个项目同时垂直与水平居中地放置在一个盒子中

指南

做出选择

要将一个盒子居中放置在另一个之中,我们需要让作为容器的盒子变成伸缩容器。再将 align-items 设置为 center 来实现块方向的轴(block axis)上的居中,并把 justify-content 设置为 center 来实现文字方向的轴(inline axis)上的居中。

将来我们可能不需要将父容器设置为伸缩容器就可以居中元素,因为此处使用的“盒子对齐”属性也被指定为适用于块布局。然而,当前在块布局上对盒子对齐属性的支持仍然是有限的,因此目前使用伸缩盒子来实现居中还是最可靠的方法。

浏览器兼容性

各种布局方法具有不同的浏览器支持。有关所使用属性的基本支持的详细信息,请参见下表

align-items

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
Supported in Flex LayoutChrome Full support 52
Full support 52
Partial support 29
Notes
Notes Older versions of the specification treat absolute positioned children as though they are a 0 by 0 flex item. Later specification versions take the children out of the flow and set their positions based on align and justify properties. Chrome implements the new behavior beginning with Chrome 52.
Full support 21
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
Edge Full support 12
Full support 12
Full support 12
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
Firefox Full support 20
Notes
Full support 20
Notes
Notes Multi-line flexbox has been supported since Firefox 28.
Full support 49
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
No support 18 — 20
Disabled
Disabled From version 18 until version 20 (exclusive): this feature is behind the layout.css.flexbox.enabled preference (needs to be set to true). To change preferences in Firefox, visit about:config.
Full support 48
Prefixed Disabled
Prefixed Implemented with the vendor prefix: -webkit-
Disabled From version 48: this feature is behind the layout.css.prefixes.webkit preference (needs to be set to true). To change preferences in Firefox, visit about:config.
IE Full support 11
Notes
Full support 11
Notes
Notes In Internet Explorer 10 and 11, if column flex items have align-items: center; set on them and their content is too large, then they will overflow the bounds of their container. See Flexbug #2.
Opera Full support 12.1Safari Full support 9
Full support 9
Full support 7
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
WebView Android Full support 52
Full support 52
Partial support 4.4
Notes
Notes Older versions of the specification treat absolute positioned children as though they are a 0 by 0 flex item. Later specification versions take the children out of the flow and set their positions based on align and justify properties. Chrome implements the new behavior beginning with Chrome 52.
Full support ≤37
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
Chrome Android Full support 52
Full support 52
Partial support 29
Notes
Notes Older versions of the specification treat absolute positioned children as though they are a 0 by 0 flex item. Later specification versions take the children out of the flow and set their positions based on align and justify properties. Chrome implements the new behavior beginning with Chrome 52.
Full support 25
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
Firefox Android Full support 20
Notes
Full support 20
Notes
Notes Multi-line flexbox has been supported since Firefox 28.
Full support 49
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
No support 18 — 20
Disabled
Disabled From version 18 until version 20 (exclusive): this feature is behind the layout.css.flexbox.enabled preference (needs to be set to true). To change preferences in Firefox, visit about:config.
Full support 48
Prefixed Disabled
Prefixed Implemented with the vendor prefix: -webkit-
Disabled From version 48: this feature is behind the layout.css.prefixes.webkit preference (needs to be set to true). To change preferences in Firefox, visit about:config.
Opera Android Full support 12.1Safari iOS Full support 9
Full support 9
Full support 7
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
Samsung Internet Android Full support 6.0
Full support 6.0
Partial support 2.0
Notes
Notes Older versions of the specification treat absolute positioned children as though they are a 0 by 0 flex item. Later specification versions take the children out of the flow and set their positions based on align and justify properties. Chrome implements the new behavior beginning with Samsung Internet 6.0.
Full support 1.5
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
Supported in Grid LayoutChrome Full support 57Edge Full support 16Firefox Full support 52IE No support NoOpera Full support 44Safari Full support 10.1WebView Android Full support 57Chrome Android Full support 52Firefox Android Full support 52Opera Android Full support 43Safari iOS Full support 10.3Samsung Internet Android Full support 6.2

Legend

Full support  
Full support
No support  
No support
See implementation notes.
See implementation notes.
User must explicitly enable this feature.
User must explicitly enable this feature.
Requires a vendor prefix or different name for use.
Requires a vendor prefix or different name for use.

justify-content

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
Supported in Flex LayoutChrome Full support 52
Full support 52
Partial support 29
Notes
Notes Older versions of the specification treat absolute positioned children as though they are a 0 by 0 flex item. Later specification versions take the children out of the flow and set their positions based on align and justify properties. Chrome implements the new behavior beginning with Chrome 52.
Full support 21
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
Edge Full support 12
Full support 12
Full support 12
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
Firefox Full support 20
Notes
Full support 20
Notes
Notes Before Firefox 27, Firefox supported only single-line flexbox.
No support 18 — 20
Disabled
Disabled From version 18 until version 20 (exclusive): this feature is behind the layout.css.flexbox.enabled preference (needs to be set to true). To change preferences in Firefox, visit about:config.
Full support 49
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
Full support 48
Prefixed Disabled
Prefixed Implemented with the vendor prefix: -webkit-
Disabled From version 48: this feature is behind the layout.css.prefixes.webkit preference (needs to be set to true). To change preferences in Firefox, visit about:config.
IE Full support 11Opera Full support 12.1Safari Full support 9
Full support 9
Full support 6.1
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
WebView Android Full support 52
Full support 52
Partial support 4.4
Notes
Notes Older versions of the specification treat absolute positioned children as though they are a 0 by 0 flex item. Later specification versions take the children out of the flow and set their positions based on align and justify properties. Chrome implements the new behavior beginning with Chrome 52.
Full support ≤37
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
Chrome Android Full support 52
Full support 52
Partial support 29
Notes
Notes Older versions of the specification treat absolute positioned children as though they are a 0 by 0 flex item. Later specification versions take the children out of the flow and set their positions based on align and justify properties. Chrome implements the new behavior beginning with Chrome 52.
Full support 25
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
Firefox Android Full support 20
Notes
Full support 20
Notes
Notes Before Firefox 27, Firefox supported only single-line flexbox.
No support 18 — 20
Disabled
Disabled From version 18 until version 20 (exclusive): this feature is behind the layout.css.flexbox.enabled preference (needs to be set to true). To change preferences in Firefox, visit about:config.
Full support 49
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
Full support 48
Prefixed Disabled
Prefixed Implemented with the vendor prefix: -webkit-
Disabled From version 48: this feature is behind the layout.css.prefixes.webkit preference (needs to be set to true). To change preferences in Firefox, visit about:config.
Opera Android Full support 12.1Safari iOS Full support 9
Full support 9
Full support 6.1
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
Samsung Internet Android Full support 6.0
Full support 6.0
Partial support 2.0
Notes
Notes Older versions of the specification treat absolute positioned children as though they are a 0 by 0 flex item. Later specification versions take the children out of the flow and set their positions based on align and justify properties. Chrome implements the new behavior beginning with Chrome 52.
Full support 1.5
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
Supported in Grid LayoutChrome Full support 57Edge Full support 16Firefox Full support 52IE No support NoOpera Full support 44Safari Full support 10.1WebView Android Full support 57Chrome Android Full support 52Firefox Android Full support 52Opera Android Full support 43Safari iOS Full support 10.3Samsung Internet Android Full support 6.2

Legend

Full support  
Full support
No support  
No support
See implementation notes.
See implementation notes.
User must explicitly enable this feature.
User must explicitly enable this feature.
Requires a vendor prefix or different name for use.
Requires a vendor prefix or different name for use.

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