关于element-ui el-backtop返回顶部组件无效问题

el-backtop绑定的盒子，需要一个滚动样式：overflow-y: scroll;

<template>
  <div id="app">
    <router-view />
    // 绑定app盒子
    <el-backtop target="#app" :visibility-height="100"></el-backtop>
  </div>
</template>

<script>
export default {
  name: "App",
  data() {
    return {};
  },
  methods: {},
  mounted() {}
};
</script>

<style>
#app {
  font-family: "Helvetica Neue", Helvetica, "PingFang SC", "Hiragino Sans GB",
    "Microsoft YaHei", "微软雅黑", Arial, sans-serif;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  width: 100%;
  height: 100%;
  /* 这里给app一个滚动效果 */
  overflow-y: scroll;
}
</style>