The animation-fill-mode property defines what values are applied by the animation outside the time it is executing.

动画有是三个状态,动画等待(animation-delay)、动画进行、动画结束。为了能够定义动画等待、动画结束时该呈现什么样式,包括默认样式、初始样式0%|from、结束样式100%|to。所以引入了animation-fill-mode:none | forwards | backwards | both