sticky
elements only stick within their direct parent's scrollable area. If the parent isn't tall enough or doesn't scroll, the sticky behavior won't be apparent for that parent.
This parent (yellow box) is short. If you scroll the main page, I won't stick relative to the *viewport* because my parent isn't the main scrolling container for that purpose. I only stick relative to Parent A's content, but Parent A has very little content to scroll past me.
Scroll down *inside this green box*. You'll see me stick to the top of *this green box*.
I am a `fixed top-0 left-0 w-full` header.
This content would be partially hidden by the `fixed` purple header if we didn't add `pt-20` (padding-top) to this container. `fixed` elements are removed from the normal document flow.