问CSS3滑动渐变动画-工作原理

EN

html {
  height: 100%
}

body {
  height: 100%;
  margin: 0
}

@keyframes loading {/* original code */
  from {/* This is the position of image of the first frame */
    background-position: -5000% 0, 0 0
  }
  to {/* This is the pos of img of the last frame */
    background-position: 5000% 0, 0 0
  }
}

@keyframes betterLoading {
  0% {/* This is the position of image of the first frame */
    background-position: -5000% 0, 0 0
  }
  50% {
    /* This is the pos of img of a frame in the middle happening animation */
    /* If duration is 1s then the pos below will be at 0.5s */
    background-position: 5000% 0, 0 0
  }
  100% {/* This is the pos of img of the last frame */
    background-position: -5000% 0, 0 0
  }
}

.skeleton {
  height: 100%;
  animation-name: betterLoading;
  animation-duration: 1.5s;
  animation-iteration-count: infinite;
  background-color: #fff;
  background-repeat: no-repeat;
  background-image: linear-gradient(90deg, hsla(0, 0%, 100%, 0), hsla(0, 0%, 100%, .8) 50%, hsla(0, 0%, 100%, 0)), linear-gradient(green 100%, transparent 0);
  background-size: 99% 100%, cover;
}

<div class="skeleton"></div>