the overflow property in HTML controls what happens in a given element when its contents extend past the element’s boundaries, in other words when the contents overflow.

Overflow has 4 possible values (AFAIK): visible, scroll, auto, and hidden, where:

visible does not clip the content and lets it extend past the parent element,

scroll clips the content and adds a scrollbar so that the user can see the rest of the content,

auto adds a scrollbar only when necessary,

and hidden clips the content that extends past the parent and doesn’t add a scrollbar.

Some paywalled/loginwalled sites load all of the article content regardless of whether the wall is up or not, so when a paywall pops up you can just go into the Inspect tool (usually CTRL+SHIFT+I) and delete the element containing the paywall, and/or, as some_random_nick said, change the article container’s overflow property from hidden to scroll, letting you see all of the content