node_modules/@vue/cli-service/lib/commands/build/demo-wc.html

<meta charset="utf-8">
<title><%- htmlWebpackPlugin.options.libName %> demo</title>
<script src="https://unpkg.com/vue@<%- htmlWebpackPlugin.options.vueMajor %>"></script>
<script src="./<%- htmlWebpackPlugin.options.libName %>.js"></script>

<% for (const comp of htmlWebpackPlugin.options.components) { %>
<<%= comp %>></<%= comp %>>
<% } %>