初始化项目，自 v1.7.1 版本开始

src/components/Backtop/index.ts

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+import Backtop from './src/Backtop.vue'
+
+export { Backtop }

src/components/Backtop/src/Backtop.vue

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+<script setup lang="ts">
+import { ElBacktop } from 'element-plus'
+import { useDesign } from '@/hooks/web/useDesign'
+
+const { getPrefixCls, variables } = useDesign()
+
+const prefixCls = getPrefixCls('backtop')
+</script>
+
+<template>
+  <ElBacktop
+    :class="`${prefixCls}-backtop`"
+    :target="`.${variables.namespace}-layout-content-scrollbar .${variables.elNamespace}-scrollbar__wrap`"
+  />
+</template>