CSS-背景圖檔 | background-image

background-image

CSS

屬性的元件上設定一個或多個背景圖像。

/* Single value */
background-image: url('https://example.com/bck.png');

/* Multiple values */
background-image: url('https://example.com/top.png'), url('https://example.com/bottom.png');

/* Keyword value */
background-image: none;

/* Global values */ 
background-image: inherit;
background-image: initial;
background-image: unset;      

背景圖像在堆疊上下文層上繪制。指定的第一個圖層被繪制為與使用者最接近。

元素的

邊界

然後被繪制在它們的頂部，然後被

background-color

繪制在它們下面。如何繪制圖像相對于框和它的邊界由

background-clip

和

background-origin

CSS屬性定義。

如果無法繪制指定的圖像（例如，無法加載指定的URI所訓示的檔案），那麼浏覽器會像處理

none

值一樣處理它。

注意：即使圖像不透明，在正常情況下也不會顯示顔色，Web開發人員應該始終指定一個

background-color

。如果圖像無法加載 - 例如，當網絡關閉時，背景顔色将被用作回退。

雙引号失敗時，單引号可能會繞過URL。

初始值	none
适用元素	all elements. It also applies to ::first-letter and ::first-line.
是否是繼承屬性	no
适用媒體	visual
計算值	as specified, but with url values made absolute
Animation type	discrete
正規順序	the unique non-ambiguous order defined by the formal grammar

文法

每個背景圖像被指定為關鍵字

none

或

<image>

值。

要指定多個背景圖檔，請提供多個值，并用逗号分隔：

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');      

值

none

是一個關鍵字表示沒有圖像。

<image>

是

<image>

表示要顯示的圖像。可以有幾個，用逗号分隔，因為支援多個背景。

正式文法

<bg-image>#where 
<bg-image> = none | <image>
where 
<image> = <url> | <image()> | <image-set()> | <element()> | <cross-fade()> | <gradient>
where 
<image()> = image( [ [ <image> | <string> ]? , <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()>
where 
<color> = <rgb()> | <rgba()> | <hsl()> | <hsla()> | <hex-color> | <named-color> | currentcolor | <deprecated-system-color>
<image-set-option> = [ <image> | <string> ] <resolution>
<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> )
where 
<rgb()> = rgb( [ [ <percentage>{3} | <number>{3} ] [ / <alpha-value> ]? ] | [ [ <percentage>#{3} | <number>#{3} ] , <alpha-value>? ] )
<rgba()> = rgba( [ [ <percentage>{3} | <number>{3} ] [ / <alpha-value> ]? ] | [ [ <percentage>#{3} | <number>#{3} ] , <alpha-value>? ] )
<hsl()> = hsl( [ <hue> <percentage> <percentage> [ / <alpha-value> ]? ] | [ <hue>, <percentage>, <percentage>, <alpha-value>? ] )
<hsla()> = hsla( [ <hue> <percentage> <percentage> [ / <alpha-value> ]? ] | [ <hue>, <percentage>, <percentage>, <alpha-value>? ] )
<side-or-corner> = [ left | right ] || [ top | bottom ]
<color-stop-list> = <color-stop>#{2,}
<ending-shape> = circle | ellipse
<size> = closest-side | farthest-side | closest-corner | farthest-corner | <length> | <length-percentage>{2}
<position> = [[ left | center | right | top | bottom | <length-percentage> ] | [ left | center | right | <length-percentage> ] [ top | center | bottom | <length-percentage> ] | [ center | [ left | right ] <length-percentage>? ] && [ center | [ top | bottom ] <length-percentage>? ]]

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

示例

請注意，星形圖像是部分透明的，并在cat圖像上分層。

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>      

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;
}      

結果

規範

Specification	Status	Comment
CSS Backgrounds and Borders Module Level 3The definition of 'background-image' in that specification.	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 1)The definition of 'background-image' in that specification.	Recommendation	From CSS1, the way images with and without intrinsic dimensions are handled is now described.
CSS Level 1The definition of 'background-image' in that specification.		Initial definition.

浏覽器相容性

Feature	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari
Basic Support	1	12	1.01	4	3.5
Multiple backgrounds			3.6	9.0	(Yes)	1.3
Gradients	1.02		3.63	10	114	4.02
SVG images	8.0				9.5	5.05
element()	No		(Yes)6
image-rect()			(Yes) -moz- 7
Any <image> value		?

	Android	Chrome for Android	Edge mobile	Firefox for Android	IE mobile	Opera Android	iOS Safari
		(Yes)2		(Yes)3		(Yes)4

1. 如果

browser.display.use_document_colors

使用者偏好

about:config

設定為

false

，則不會顯示背景圖像。

2. 某些版本僅支援以

-webkit

，

-moz

，或為

-o

字首的實驗性漸變。