Scoped style does not apply to pseudo layers in advanced background

[yhatt]

Whenever using ![bg]() syntax in advanced background mode, section::before and section::after selectors by setting <style scoped> will not work due to lacked attribute for scoping in <section> element for the pseudo layer.

<!-- paginate: true -->

<style scoped>
section::after {
  color: red;
}
</style>

---

![bg](https://marp.app/assets/hero-background.svg)

<style scoped>
section::after {
  color: red;
}
</style>

In this Markdown, a page number of the second slide will not turn the color to red if enabled advanced background through new Marpit({ inlineSVG: true }).