I find that I cannot use more than one component in one vue file.

If I am using Codesandbox, everything works fine
https://codesandbox.io/s/keen-surf-3ww6o?file=/src/App.vue

When I inspect in Chrome, a strange comment is shown.

App.vue

<template>
  <div id="app">
    <Step />
  </div>
</template>

<script>
import Vue from "vue";
const Step = Vue.component("step", {
  template: `<div>
    <h1>Hello world</h1>
  </div>`,
  props: {
    id: Number,
    description: String,
  },
});
export default {
  name: "App",
  components: {
    Step,
  },
};
</script>

<style>
#app {
  font-family: "Avenir", Helvetica, Arial, sans-serif;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  text-align: center;
  color: #2c3e50;
  margin-top: 60px;
}
</style>