Why the iframe's content affects the CSS of the page where it is located?

Insert on the page of the website js-widget affiliate program.
Inside this widget loaded fonts c fonts.googleapis.com.

As a result, when you refresh the page with the widget at the end of the page load (when the widget is loaded) change the heading styles (h1, h2, etc.).

To check the domain has been added fonts.googleapis.com in the hosts file (0.0.0.0), then the styles on the page with the widget do not change.

Why is this happening? Why the contents of the iframe to change the page which is the iframe? And how to deactivate this?

ps.
I apologize and thank you for the offer to check again, iframe or not.
first encountered this, so there is no iframe.
June 26th 19 at 14:22
3 answers
June 26th 19 at 14:24
Solution
Code of the insertion? What makes You think that it's iframe?
June 26th 19 at 14:26
Solution
Code of the insertion in the Studio
June 26th 19 at 14:28
Solution
Maybe it's not an iframe.

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