1、首先给 标签关闭动画效果  :collapse-transition = "false"

<el-menu :default-active="$route.path"
         class="el-menu-vertical-demo"
         :collapse="isCollapse"
         background-color="#40586F"
         text-color="#fff"
         active-text-color="#409eff"
         :collapse-transition = "false"
         :unique-opened="true"
         router>
</ el-menu>

2、然后给侧边栏添加自定义 动画

<style scoped>
    .el-aside {
      background: $primary-color;
      transition: width 0.15s;
      -webkit-transition: width 0.15s;
      -moz-transition: width 0.15s;
      -webkit-transition: width 0.15s;
      -o-transition: width 0.15s;
    }
</style>