Hide UI element of a webpage from other page [wordpress]

i'm new to web and facing issue while hiding a UI element in a webpage from another webpage. Scenario:

1. I've a WordPress site (Theme-TwentySeventeen).
2. I've added a Logout button programmatically on page as shown in image.
3. I've multiple posts, and every post has a button (play video).
4. When user taps on Play Video button, an iframe appears (fancybox). It has another button "Login".
5. I want to show/hide Logout button on main page based on the click on "Login" button in iFrame.

I tried to access Logout button using it's ID from iFrame. But it's not part of iFrame source code. and i was not able to access it.

P.S. I can show/hide logout button from the main page using JQuery.

Query: Is there any way in web to pass notification from one page to other pages? Please guide