backdrop-filter
===============

**`backdrop-filter`** CSS 属性可以让你为一个元素后面区域添加图形效果（如模糊或颜色偏移）。因为它适用于元素*背后*的所有元素，为了看到效果，必须使元素或其背景至少部分透明。


```css
/\* 关键词值 \*/
backdrop-filter: none;

/\* 指向 SVG 滤镜的 URL \*/
backdrop-filter: url(commonfilters.svg#filter);

/\* <filter-function> 滤镜函数值 \*/
backdrop-filter: blur(2px);
backdrop-filter: brightness(60%);
backdrop-filter: contrast(40%);
backdrop-filter: drop-shadow(4px 4px 10px blue);
backdrop-filter: grayscale(30%);
backdrop-filter: hue-rotate(120deg);
backdrop-filter: invert(70%);
backdrop-filter: opacity(20%);
backdrop-filter: sepia(90%);
backdrop-filter: saturate(80%);

/\* 多重滤镜 \*/
backdrop-filter: url(filters.svg#filter) blur(4px) saturate(150%);

/\* 全局值 \*/
backdrop-filter: inherit;
backdrop-filter: initial;
backdrop-filter: revert;
backdrop-filter: unset;
```

语法
--

### 值

`none`

没有应用于背景的滤镜。

`<filter-function-list>`

一个以空格分隔的滤镜函数（`<filter-function>`）或是要应用到背景上的 SVG 滤镜。

形式化定义
-----

|  |  |
| --- | --- |
| 初始值 | `none` |
| 适用元素 | all elements; In SVG, it applies to container elements excluding the `defs` element and all graphics elements |
| 是否是继承属性 | 否 |
| 计算值 | as specified |
| Animation type | a filter function list |

形式化语法
-----
```

backdrop-filter =   
  none                 |  
  <filter-value-list>    
  
<filter-value-list> =   
  [ <filter-function> | <url> ]+    
  
<filter-function> =   
  <blur()>         |  
  <brightness()>   |  
  <contrast()>     |  
  <drop-shadow()>  |  
  <grayscale()>    |  
  <hue-rotate()>   |  
  <invert()>       |  
  <opacity()>      |  
  <sepia()>        |  
  <saturate()>       
  
<url> =   
  <url()>  |  
  <src()>    
  
<blur()> =   
  blur( <length>? )    
  
<brightness()> =   
  brightness( [ <number> | <percentage> ]? )    
  
<contrast()> =   
  contrast( [ <number> | <percentage> ]? )    
  
<drop-shadow()> =   
  drop-shadow( [ <color>? && <length>{2,3} ] )    
  
<grayscale()> =   
  grayscale( [ <number> | <percentage> ]? )    
  
<hue-rotate()> =   
  hue-rotate( [ <angle> | <zero> ]? )    
  
<invert()> =   
  invert( [ <number> | <percentage> ]? )    
  
<opacity()> =   
  opacity( [ <number> | <percentage> ]? )    
  
<sepia()> =   
  sepia( [ <number> | <percentage> ]? )    
  
<saturate()> =   
  saturate( [ <number> | <percentage> ]? )    
  
<url()> =   
  url( <string> <url-modifier>\* )  |  
  <url-token>                        
  
<src()> =   
  src( <string> <url-modifier>\* )    
  
```

示例
--

### CSS


```css
.box {
  background-color: rgba(255, 255, 255, 0.3);
  border-radius: 5px;
  font-family: sans-serif;
  text-align: center;
  line-height: 1;
  -webkit-backdrop-filter: blur(10px);
  backdrop-filter: blur(10px);
  max-width: 50%;
  max-height: 50%;
  padding: 20px 40px;
}

html,
body {
  height: 100%;
  width: 100%;
}

body {
  background-image: url(https://picsum.photos/id/1080/6858/4574),
    linear-gradient(rgb(219, 166, 166), rgb(0, 0, 172));
  background-position: center center;
  background-repeat: no-repeat;
  background-size: cover;
}

.container {
  align-items: center;
  display: flex;
  justify-content: center;
  height: 100%;
  width: 100%;
}
```

### HTML


```html
<div class="container">
  <div class="box">
    <p>backdrop-filter: blur(10px)</p>
  </div>
</div>
```

### 结果

规范
--

| Specification |
| --- |
| Filter Effects Module Level 2 # BackdropFilterProperty |

浏览器兼容性
------

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参见
--

* `filter`