Fix

docs/.vitepress/theme/index.js

@@ -0,0 +1,11 @@
+import CopyButton from 'vitepress-copy-helper';
+import 'vitepress-copy-helper/style.css'
+import DefaultTheme from 'vitepress/theme'
+
+/** @type {import('vitepress').Theme} */
+export default {
+  extends: DefaultTheme,
+  enhanceApp({ app }) {
+    app.component('C', CopyButton)
+  }
+}