Why does css written in components end up in after build?

Question

Vue.js

Hello. I assembled the vue component library using rollup, I import it into the application: The button itself looks something like this, simplified for example:

import { VButton } from '@compnany/ui';

<template>
  <button class="v-button">
      <slot/>
  </button>
</template>

<script>
export default {}
</script>

<style lang="postcss">
.v-button {
  background-color: red;
}
.v-button:hover {
  background-color: blue;
}
</style>

Everything works great, though! For some reason, I'm doing a build of the project, the css of the component gets into <style>the page tag, and not into the css file. The project is deployed on vue-cli latest version.

Ideally, I would like the css of a particular component to get into the page bundle (I use lazy load in router).