animation

Baseline Widely available *

This feature is well established and works across many devices and browser versions. It’s been available across browsers since September 2015.

* Some parts of this feature may have varying levels of support.

CSS animation 属性是 animation-name，animation-duration, animation-timing-function，animation-delay，animation-iteration-count，animation-direction，animation-fill-mode 和 animation-play-state 属性的一个简写属性形式。

尝试一下

animation: 3s ease-in 1s infinite reverse both running slidein;

animation: 3s linear 1s infinite running slidein;

animation: 3s linear 1s infinite alternate slidein;

animation: 0.5s linear 1s infinite alternate slidein;

<section class="flex-column" id="default-example">
  <div id="example-element"></div>
</section>

#example-element {
  background-color: #1766aa;
  margin: 20px;
  border: 5px solid #333;
  width: 150px;
  height: 150px;
  border-radius: 50%;
}

@keyframes slidein {
  from {
    margin-left: -20%;
  }
  to {
    margin-left: 100%;
  }
}

语法

css
/* @keyframes duration | easing-function | delay |
iteration-count | direction | fill-mode | play-state | name */
animation: 3s ease-in 1s 2 reverse both paused slidein;

/* @keyframes duration | easing-function | delay | name */
animation: 3s linear 1s slidein;

/* two animations */
animation:
  3s linear slidein,
  3s ease-out 5s slideout;

animation 属性用来指定一组或多组动画，每组之间用逗号相隔。

每组动画规定的属性如下：

每个动画定义中的属性值的顺序很重要：可以被解析为 <time> 的第一个值被分配给animation-duration，第二个分配给 animation-delay。

每个动画定义中的值的顺序，对于区分 animation-name 值与其他关键字也很重要。解析时，对于除 animation-name 之外的有效的关键字，必须被前面的简写中没有找到值的属性所接受。此外，在序列化时，animation-name 与以及其他属性值做区分等情况下，必须输出其他属性的默认值。

Values

<single-animation-iteration-count>

动画播放的次数。该值必须是animation-iteration-count可用的值之一。

<single-animation-direction>

动画播放的方向。该值必须是animation-direction可用的值之一。

<single-animation-fill-mode>

确定动画在执行之前和之后这两个阶段应用的样式。该值必须是animation-fill-mode可用的值之一。

<single-animation-play-state>

确定动画是否正在播放。该值必须是animation-play-state中可用的值之一。

语法

animation = 
  <single-animation>#  

<single-animation> = 
  <time [0s,∞]>                       ||
  <easing-function>                   ||
  <time>                              ||
  <single-animation-iteration-count>  ||
  <single-animation-direction>        ||
  <single-animation-fill-mode>        ||
  <single-animation-play-state>       ||
  [ none | <keyframes-name> ]         

<easing-function> = 
  <linear-easing-function>        |
  <cubic-bezier-easing-function>  |
  <step-easing-function>          

<single-animation-iteration-count> = 
  infinite        |
  <number [0,∞]>  

<single-animation-direction> = 
  normal             |
  reverse            |
  alternate          |
  alternate-reverse  

<single-animation-fill-mode> = 
  none       |
  forwards   |
  backwards  |
  both       

<single-animation-play-state> = 
  running  |
  paused   

<keyframes-name> = 
  <custom-ident>  |
  <string>        

<linear-easing-function> = 
  linear      |
  <linear()>  

<cubic-bezier-easing-function> = 
  ease              |
  ease-in           |
  ease-out          |
  ease-in-out       |
  <cubic-bezier()>  

<step-easing-function> = 
  step-start  |
  step-end    |
  <steps()>   

<linear()> = 
  linear( [ <number> && <percentage>{0,2} ]# )  

<cubic-bezier()> = 
  cubic-bezier( [ <number [0,1]> , <number> ]#{2} )  

<steps()> = 
  steps( <integer> , <step-position>? )  

<step-position> = 
  jump-start  |
  jump-end    |
  jump-none   |
  jump-both   |
  start       |
  end

示例

赛隆人之眼

html
<div class="view_port">
  <div class="polling_message">Listening for dispatches</div>
  <div class="cylon_eye"></div>
</div>
css
.polling_message {
  color: white;
  float: left;
  margin-right: 2%;
}

.view_port {
  background-color: black;
  height: 25px;
  width: 100%;
  overflow: hidden;
}

.cylon_eye {
  background-color: red;
  background-image: linear-gradient(
    to right,
    rgba(0, 0, 0, 0.9) 25%,
    rgba(0, 0, 0, 0.1) 50%,
    rgba(0, 0, 0, 0.9) 75%
  );
  color: white;
  height: 100%;
  width: 20%;

  -webkit-animation: 4s linear 0s infinite alternate move_eye;
  animation: 4s linear 0s infinite alternate move_eye;
}

@-webkit-keyframes move_eye {
  from {
    margin-left: -20%;
  }
  to {
    margin-left: 100%;
  }
}
@keyframes move_eye {
  from {
    margin-left: -20%;
  }
  to {
    margin-left: 100%;
  }
}

更多示例请参阅使用 CSS 动画。

潜在的问题

眨眼和闪烁的动画对于有认知问题的人来说是有问题的，比如注意力缺陷多动障碍 (ADHD)。此外，某些动画效果可以触发前庭神经紊乱、癫痫、偏头痛和暗点敏感性。

考虑提供一种暂停或禁用动画的机制，以及使用 Reduced Motion Media Query（简约运动媒体查询），为那些表示不喜欢动画的用户创建一个良好的体验。

规范

Specification
CSS Animations Level 1
# animation

浏览器兼容性

参见