UPDATE

src/App.vue

 <script setup>
-import HelloWorld from './components/HelloWorld.vue'
-import TheWelcome from './components/TheWelcome.vue'
+
 </script>
 
 <template>
-  <header>
-    <img alt="Vue logo" class="logo" src="./assets/logo.svg" width="125" height="125" />
-
-    <div class="wrapper">
-      <HelloWorld msg="You did it!" />
-    </div>
-  </header>
-
-  <main>
-    <TheWelcome />
-  </main>
+  
 </template>
 
 <style scoped>
-header {
-  line-height: 1.5;
-}
-
-.logo {
-  display: block;
-  margin: 0 auto 2rem;
-}
-
-@media (min-width: 1024px) {
-  header {
-    display: flex;
-    place-items: center;
-    padding-right: calc(var(--section-gap) / 2);
-  }
-
-  .logo {
-    margin: 0 2rem 0 0;
-  }
-
-  header .wrapper {
-    display: flex;
-    place-items: flex-start;
-    flex-wrap: wrap;
-  }
-}
 </style>

src/page/child.vue

+<script setup>
+import { defineEmits } from 'vue';
+const emit = defineEmits(["value"])
+</script>
+
+<template>
+  <button @click="add">点我加一</button>
+</template>
+
+<style scoped>
+</style>
\ No newline at end of file

src/page/parent.vue

+<script setup>
+import child from './child.vue';
+</script>
+
+<template>
+  <child></child>
+</template>
+
+<style scoped>
+</style>
\ No newline at end of file