动画实现简洁 loading 效果

.loading:after {
  display: inline-block;
  overflow: hidden;
  vertical-align: bottom;
  content: "\2026";
  -webkit-animation: ellipsis 2s infinite;
}

// 动画部分
@-webkit-keyframes ellipsis {
  from {
    width: 2px;
  }
  to {
    width: 15px;
  }
}