How to add customer HTML after “post_1” (part2)

Support
3

All together it will be something like this?

<script type="text/discourse-plugin" version="0.8">
api.decorateWidget("post:after", helper => {
  const firstPost = helper.attrs.firstPost;
  const h = helper.h;
  if (firstPost) {
    return h("div#custom-ad", [
      h(
        "a.custom-ad-link",
        { href: "example.com" },
        h("img", { src: "https://picsum.photos/id/74/750/90" })
      )
    ]);
  }
});
</script>
#custom-ad {
  .custom-ad-link {
    img {
      width: 100%;
    }
  }
}
#custom-ad {
  max-width: calc(45px + 690px + (11px * 2));
}