How does the frontend framework "detection" when browsing files work?

I’ve noticed that when debugging files on a random web app, a small icon next to the file name is shown. That icon displays the frontend framework being used in that website, and I think it’s really cool. For example, when inspecting a file on, a news website:

Those sort of frontend frameworks usually have a “production mode”, and this detection works even with this “production mode”.
My question is - How does this “detection” work, and what is the rationale behind having this as a feature?
I quite like it and am curious to learn how it works.