background-image

CSS background-image 属性用于为一个元素设置一个或者多个背景图像。

在绘制时,图像以 z 方向堆叠的方式进行。先指定的图像会在之后指定的图像上面绘制。因此指定的第一个图像“最接近用户”。

然后元素的边框 border 会在它们之上被绘制,而 background-color 会在它们之下绘制。图像的绘制与盒子以及盒子的边框的关系,需要在CSS属性background-clipbackground-origin 中定义。

如果一个指定的图像无法被绘制 (比如,被指定的 URI 所表示的文件无法被加载),浏览器会将此情况等同于其值被设为 none

注意: 即使图像是不透明的,背景色在通常情况下并不会被显示,web开发者仍然应该指定 background-color 属性。如果图像无法被加载—例如,在网络连接断开的情况下—背景色就会被绘制。

语法

每个背景图像被明确规定为关键字 none 或是一个 <image> 值。

可以提供由逗号分隔的多个值来指定多个背景图像:

background-image:
  linear-gradient(to bottom, rgba(255,255,0,0.5), rgba(0,0,255,0.5)),
  url('https://mdn.mozillademos.org/files/7693/catfront.png');

取值

none
是一个表示无背景图的关键字。
<image>
<image> 用来标记将要显示的图片. 支持多背景设置,背景之间以逗号隔开.

正规语法

<bg-image>#

where
<bg-image> = none | <image>

where
<image> = <url> | <image()> | <image-set()> | <element()> | <cross-fade()> | <gradient>

where
<image()> = image( <image-tags>? [ <image-src>? , <color>? ]! )
<image-set()> = image-set( <image-set-option># )
<element()> = element( <id-selector> )
<cross-fade()> = cross-fade( <cf-mixing-image> , <cf-final-image>? )
<gradient> = <linear-gradient()> | <repeating-linear-gradient()> | <radial-gradient()> | <repeating-radial-gradient()> | <conic-gradient()>

where
<image-tags> = ltr | rtl
<image-src> = <url> | <string>
<color> = <rgb()> | <rgba()> | <hsl()> | <hsla()> | <hex-color> | <named-color> | currentcolor | <deprecated-system-color>
<image-set-option> = [ <image> | <string> ] <resolution>
<id-selector> = <hash-token>
<cf-mixing-image> = <percentage>? && <image>
<cf-final-image> = <image> | <color>
<linear-gradient()> = linear-gradient( [ <angle> | to <side-or-corner> ]? , <color-stop-list> )
<repeating-linear-gradient()> = repeating-linear-gradient( [ <angle> | to <side-or-corner> ]? , <color-stop-list> )
<radial-gradient()> = radial-gradient( [ <ending-shape> || <size> ]? [ at <position> ]? , <color-stop-list> )
<repeating-radial-gradient()> = repeating-radial-gradient( [ <ending-shape> || <size> ]? [ at <position> ]? , <color-stop-list> )
<conic-gradient()> = conic-gradient( [ from <angle> ]? [ at <position> ]?, <angular-color-stop-list> )

where
<rgb()> = rgb( <percentage>{3} [ / <alpha-value> ]? ) | rgb( <number>{3} [ / <alpha-value> ]? ) | rgb( <percentage>#{3} , <alpha-value>? ) | rgb( <number>#{3} , <alpha-value>? )
<rgba()> = rgba( <percentage>{3} [ / <alpha-value> ]? ) | rgba( <number>{3} [ / <alpha-value> ]? ) | rgba( <percentage>#{3} , <alpha-value>? ) | rgba( <number>#{3} , <alpha-value>? )
<hsl()> = hsl( <hue> <percentage> <percentage> [ / <alpha-value> ]? ) | hsl( <hue>, <percentage>, <percentage>, <alpha-value>? )
<hsla()> = hsla( <hue> <percentage> <percentage> [ / <alpha-value> ]? ) | hsla( <hue>, <percentage>, <percentage>, <alpha-value>? )
<side-or-corner> = [ left | right ] || [ top | bottom ]
<color-stop-list> = [ <linear-color-stop> [, <linear-color-hint>]? ]# , <linear-color-stop>
<ending-shape> = circle | ellipse
<size> = closest-side | farthest-side | closest-corner | farthest-corner | <length> | <length-percentage>{2}
<position> = [ [ left | center | right ] || [ top | center | bottom ] | [ left | center | right | <length-percentage> ] [ top | center | bottom | <length-percentage> ]? | [ [ left | right ] <length-percentage> ] && [ [ top | bottom ] <length-percentage> ] ]
<angular-color-stop-list> = [ <angular-color-stop> [, <angular-color-hint>]? ]# , <angular-color-stop>

where
<alpha-value> = <number> | <percentage>
<hue> = <number> | <angle>
<linear-color-stop> = <color> <color-stop-length>?
<linear-color-hint> = <length-percentage>
<length-percentage> = <length> | <percentage>
<angular-color-stop> = <color> && <color-stop-angle>?
<angular-color-hint> = <angle-percentage>

where
<color-stop-length> = <length-percentage>{1,2}
<color-stop-angle> = <angle-percentage>{1,2}
<angle-percentage> = <angle> | <percentage>

示例

注意星星图片部分透明且位于猫图片上方.

HTML

<div>
  <p class="catsandstars">
    This paragraph is full of cats<br />and stars.
  </p>
  <p>This paragraph is not.</p>
  <p class="catsandstars">
    Here are more cats for you.<br />Look at them!
  </p>
  <p>And no more.</p>
</div>

CSS

p {
  font-size: 1.5em;
  color: #FE7F88;
  background-image: none;
  background-color: transparent;
}

div {
  background-image:
      url("https://mdn.mozillademos.org/files/6457/mdn_logo_only_color.png");
}

.catsandstars {
  background-image:
      url("https://mdn.mozillademos.org/files/11991/startransparent.gif"), 
      url("https://mdn.mozillademos.org/files/7693/catfront.png");
  background-color: transparent;
}

Result

可访问性相关

浏览器不会向辅助技术提供有关背景图像的任何特殊信息。这对于屏幕阅读器来说非常重要,因为屏幕阅读器不会告知用户它的存在,因而不能向用户传达任何信息。如果图像包含对理解页面总体目的至关重要的信息,则最好在文档中作出语义性地描述(describe it semantically)。

规范

Specification Status Comment
CSS Backgrounds and Borders Module Level 3
background-image
Candidate Recommendation From CSS2 Revision 1, the property has been extended to support multiple backgrounds and any <image> CSS data type.
CSS Level 2 (Revision 2)
background-image
Working Draft From CSS1, the way images with and without intrinsic dimensions are handled is now described.
CSS Level 1
background-image
Recommendation Initial definition.
初始值none
适用元素all elements. It also applies to ::first-letter and ::first-line.
是否是继承属性
适用媒体visual
计算值as specified, but with url values made absolute
Animation typediscrete
正规顺序the unique non-ambiguous order defined by the formal grammar

浏览器兼容性

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
background-imageChrome Full support 1Edge Full support 12Firefox Full support 1
Notes
Full support 1
Notes
Notes If the browser.display.use_document_colors user preference in about:config is set to false, background images will not be displayed.
IE Full support 4Opera Full support 3.5Safari Full support 1WebView Android Full support ≤37Chrome Android Full support 18Firefox Android Full support 4
Notes
Full support 4
Notes
Notes If the browser.display.use_document_colors user preference in about:config is set to false, background images will not be displayed.
Opera Android Full support YesSafari iOS Full support 1Samsung Internet Android Full support Yes
element()
Experimental
Chrome No support NoEdge No support NoFirefox Full support 4
Prefixed
Full support 4
Prefixed
Prefixed Implemented with the vendor prefix: -moz-
IE No support NoOpera No support NoSafari No support NoWebView Android No support NoChrome Android No support NoFirefox Android Full support 4
Prefixed
Full support 4
Prefixed
Prefixed Implemented with the vendor prefix: -moz-
Opera Android No support NoSafari iOS No support NoSamsung Internet Android No support No
GradientsChrome Full support 1
Notes
Full support 1
Notes
Notes Some versions support only experimental gradients prefixed with -webkit.
Edge Full support 12Firefox Full support 3.6
Notes
Full support 3.6
Notes
Notes Some versions support only experimental gradients prefixed with -moz.
IE Full support 10Opera Full support 11
Notes
Full support 11
Notes
Notes Some versions support only experimental gradients prefixed with -o.
Safari Full support 4
Notes
Full support 4
Notes
Notes Some versions support only experimental gradients prefixed with -webkit.
WebView Android Full support ≤37
Notes
Full support ≤37
Notes
Notes Some versions support only experimental gradients prefixed with -webkit.
Chrome Android Full support 18
Notes
Full support 18
Notes
Notes Some versions support only experimental gradients prefixed with -webkit.
Firefox Android Full support 4
Notes
Full support 4
Notes
Notes Some versions support only experimental gradients prefixed with -moz.
Opera Android Full support Yes
Notes
Full support Yes
Notes
Notes Some versions support only experimental gradients prefixed with -o.
Safari iOS Full support 3.2
Notes
Full support 3.2
Notes
Notes Some versions support only experimental gradients prefixed with -webkit.
Samsung Internet Android Full support Yes
image-rect()
Experimental
Chrome No support NoEdge No support NoFirefox Full support 4
Prefixed
Full support 4
Prefixed
Prefixed Implemented with the vendor prefix: -moz-
IE No support NoOpera No support NoSafari No support NoWebView Android No support NoChrome Android No support NoFirefox Android Full support 4
Prefixed
Full support 4
Prefixed
Prefixed Implemented with the vendor prefix: -moz-
Opera Android No support NoSafari iOS No support NoSamsung Internet Android No support No
image-set()
Experimental
Chrome Full support 21
Prefixed
Full support 21
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
Edge No support NoFirefox No support No
Notes
No support No
Notes
Notes See bug 1107646.
IE No support NoOpera Full support 15
Prefixed
Full support 15
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
Safari Partial support 6
Prefixed Notes
Partial support 6
Prefixed Notes
Prefixed Implemented with the vendor prefix: -webkit-
Notes Support for url images only and x is the only supported resolution unit. See bug 160934.
WebView Android Full support 4.4
Prefixed
Full support 4.4
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
Chrome Android Full support 25
Prefixed
Full support 25
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
Firefox Android No support No
Notes
No support No
Notes
Notes See bug 1107646.
Opera Android Full support 14
Prefixed
Full support 14
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
Safari iOS Partial support 6
Prefixed Notes
Partial support 6
Prefixed Notes
Prefixed Implemented with the vendor prefix: -webkit-
Notes Support for url images only and x is the only supported resolution unit. See bug 160934.
Samsung Internet Android Full support 4.0
Prefixed
Full support 4.0
Prefixed
Prefixed Implemented with the vendor prefix: -webkit-
Multiple backgroundsChrome Full support 1Edge Full support 12Firefox Full support 3.6IE Full support 9Opera Full support YesSafari Full support 1.3WebView Android Full support ≤37Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support YesSafari iOS Full support 1Samsung Internet Android Full support Yes
SVG imagesChrome Full support 8Edge Full support 12Firefox Full support 4IE Full support 9Opera Full support 9.5Safari Full support 5
Notes
Full support 5
Notes
Notes Support of SVG in CSS background is incomplete.
WebView Android Full support ≤37Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support YesSafari iOS Full support 5
Notes
Full support 5
Notes
Notes Support of SVG in CSS background is incomplete.
Samsung Internet Android Full support Yes

Legend

Full support  
Full support
Partial support  
Partial support
No support  
No support
Experimental. Expect behavior to change in the future.
Experimental. Expect behavior to change in the future.
See implementation notes.
See implementation notes.
Requires a vendor prefix or different name for use.
Requires a vendor prefix or different name for use.

[1] If the browser.display.use_document_colors user preference in about:config is set to false, background images will not de displayed.

[2] Support of SVG in CSS background is incomplete in the current version of iOS Safari (5.0). The same for Safari prior 5.0.

参见