背景 | background

CSS background速记属性允许您一次调整所有可用的背景样式选项，包括彩色图像，原点和大小，重复方法以及其他功能。background可用于对一个或多个设置值：background-clip，background-color，background-image，background-origin，background-position，background-repeat，background-size，和background-attachment。

/* Using a <background-color> */
background: green;

/* Using a <bg-image> and <repeat-style> */
background: url("test.jpg") repeat-y;

/* Using a <box> and <background-color> */
background: border-box red;

/* A single image, centered and scaled */
background: no-repeat center/80% url("../img/image.png");

backgroundCSS简写属性明确分配给定的值，并设置缺少的属性为初始值。

• background-image: none
• background-position: 0% 0%
• background-size: auto auto
• background-repeat: repeat
• background-origin: padding-box
• background-clip: border-box
• background-attachment: scroll
• background-color: transparent

Applies to all elements. It also applies to [`::first-letter`](::first-letter) and [`::first-line`](::first-line).   [Inherited](inheritance) no   Percentages as each of the properties of the shorthand:

• background-position：指背景定位区域的大小减去背景图像的大小; 大小是指水平偏移的宽度和垂直偏移的高度
• background-size：相对于背景定位区域

Media visual   [Computed value](computed_value) as each of the properties of the shorthand:

• background-image：如指定的那样，但是具有url绝对值
• background-position：一个列表，每个项目由两个关键字组成，代表原点和来自该原点的两个偏移量，每个以绝对长度给出（如果给定 <length>），否则以百分比
• background-size：按照规定，但相对长度转换为绝对长度
• background-repeat：一个列表，每个项目由两个关键字组成，每个维度一个
• background-origin： 作为指定
• background-clip： 作为指定
• background-attachment： 作为指定
• background-color：计算颜色

Animation type as each of the properties of the shorthand:

• background-color：一种颜色
• background-image：离散
• background-clip：离散
• background-position：长度，百分比或计算的简单列表的可重复列表
• background-size：长度，百分比或计算的简单列表的可重复列表
• background-repeat：离散
• background-attachment：离散

Canonical order order of appearance in the formal grammar of the values  

句法

background属性被指定为一个或多个背景层，用逗号分隔。

每个图层的语法如下所示：

• 每个图层可能包含零个或一个以下任何值：
  • <attachment>
  • <bg-image>
  • <position>
  • <bg-size>
  • <repeat-style>
• <bg-size>值可能仅在紧跟在<position>“/”字符之后，如下所示：“ center/80%”。
• <box>值可能包含零次，一次或两次。如果包含一次，它会同时设置background-origin和background-clip。如果它包含两次，第一次出现background-origin，第二次background-clip。
• <background-color>值可能只包含在指定的最后一个图层中。

值

<attachment>参见background-attachment<box>参见background-clip和background-origin<background-color>参见background-color<bg-image>参见background-image<position>参见background-position<repeat-style>参见background-repeat<bg-size>参见background-size。

形式语法

[ <bg-layer> , ]* <final-bg-layer>where <bg-layer> = <bg-image> || <position> [ / <bg-size> ]? || <repeat-style> || <attachment> || <box>{1,2}<final-bg-layer> = <bg-image> || <position> [ / <bg-size> ]? || <repeat-style> || <attachment> || <box> || <box> || <'background-color'>where <bg-image> = none | <image><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>? ]]<bg-size> = [ <length-percentage> | auto ]{1,2} | cover | contain<repeat-style> = repeat-x | repeat-y | [ repeat | space | round | no-repeat ]{1,2}<attachment> = scroll | fixed | local<box> = border-box | padding-box | content-boxwhere <image> = <url> | <image()> | <image-set()> | <element()> | <cross-fade()> | <gradient><length-percentage> = <length> | <percentage>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}where <alpha-value> = <number> | <percentage><hue> = <number> | <angle><color-stop> = <color> <length-percentage>?

示例

HTML

<p class="topbanner">
  Starry sky<br/>
  Twinkle twinkle<br/>
  Starry sky
</p>
<p class="warning">Here is a paragraph<p>

CSS

.warning { 
  background: pink; 
}

.topbanner { 
  background: url("https://mdn.mozillademos.org/files/11983/starsolid.gif") #99f repeat-y fixed; 
}

结果

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规范

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