Request for improvement

Thank you for a great plugin!

It does exactly what I need.
However, there is one issue I faced.

The thing is, I only need it to work on a specific page with an article.
Here is a test page with plugin implemented:
https://vl-sciencefiction.space/science-fiction-story-1/

This is a page with a story and I wanted to improve usability by letting users choose the font size. It works. However, if a user increases the font size and then goes to some other page, the font is increased there too, which is not expected there.
Please refer to this video:
https://www.screenpresso.com/=Z13se

I can see different alternatives on how to fix that:

1. In admin area, create a setting that switches ON/OFF cookie logic
2. In admin area, create a field to set a specific CSS class or ID, for which the widget will be forking
3. In admin area, allow users to activate widget for particular page(s) alone
4. By default, put the plugin script only to those pages that do have short-code (might be the best approach, since other pages won’t have unused JS any longer)

If possible, could you please implement any of these above, or suggest another solution?

Many, many thanks!

The page I need help with: [log in to see the link]