How to write your own styles for RSS feeds

I've been using RSS.app to create the RSS feed for Instagram posts. I did customize the widgets through their website as close as I could but it's not there the way the client wants. So I thought of writing my custom CSS for the RSS feed.

So I guess my question is, is there any way I could write my own styles for that RSS feed. If not, then is there a website where I could generate and style the RSS feed according to my own liking.

The reason I'm using RSS.app is because it allows you to create a feed by using a public Instagram account without asking for credentials of clients' account.

Below is the customized RSS feed that I generated from their website. Here is a codeSandbox

<rssapp-wall id="FBJdgbQhIgkwCJp3"></rssapp-wall>
    <script
      src="https://widget.rss.app/v1/wall.js"
      type="text/javascript"
      async
    ></script>

And this is the design I'm hoping to create.

Please any help or suggestions would be appreciated. Thanks!

Solution

You could just use the API resource and build your own DOM, which might be simpler then hacking away at the dom generated by the web component.

<pre id="feed"></pre>
<script>
  fetch("https://rss.app/api/widget/wall/FBJdgbQhIgkwCJp3?")
    .then(res => res.json())
    .then(v => document.getElementById("feed").innerHTML = JSON.stringify(v,null,2)
  );
</script>