Scroll boundary

A scroll boundary is the point at which a scrollable element cannot be scrolled any further in a particular direction, either at the top or bottom (or left/right for horizontal scrolling). This typically is the edge of the scrollport.

When the content of a scroll container does not exceed the container size in the scrolling direction, the container is considered to be at its scroll boundary at all times. This is because there’s no extra content to scroll through. If the content is prevented from scrolling, such as when overflow: hidden is set, the element is not a scroll container, and therefore, there is no scroll boundary.