http://www.w3cplus.com/content/css3-animation
@-webkit-keyframes 'test' {
0% {}
50% {}
100% {}
}
-webkit-animation:'test' 2s linear 1s infinite alternate
-webkit-animation:name duration timing-function delay iteration-count direction
animation-iteration-count:次数/infinite(无限次)
animation-direction:normal/alternate(偶数次向前，奇数次反方向)
animation-fill-mode:forwards(动画结束时的状态)
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animation-play-state:running(运动)、paused(暂停) =>越少使用