Creating a theme escaped block

I’m looking to find a way of including properly formatted screenplays on my site. Previously I used a Wordpress plugin called Scrippets that would convert a special markup called Fountain to be properly displayed on the site.

I’ve found a way to covert fountain files to HTML. This is where I need a bit of help. The HTML file has some very specific styles that if were allowed to apply to rest of the site would mess with the layout.

One option I have is to just embed the HTML as an iframe (HTML file located in an s3 bucket), but as far as I know, this is bad for SEO.

Is there a way to embed an HTML file directly without the theme styles applying to that HTML and vice versa?