Why Doesn't `bottom:0` Make My `position:sticky` Element Stick Immediately?

Why "bottom:0" Doesn't Seem to Work with Position:Sticky

When attempting to use "bottom:0" with "position:sticky," it may initially appear that the element is not becoming sticky. However, this is not the case. To understand this behavior, let's examine the definition of "sticky."

According to the CSS specification, an element with "position:sticky" remains positioned relative until its containing block crosses a threshold. In this scenario, the containing block is the pink "block" element.

When setting "bottom:0," the "move" element will become sticky when the bottom of the containing block becomes visible within the browser window. However, in your test code, the "block" element has a height of 200px, and the "move" element is placed inside it. This means that by default, the "move" element is already positioned at the bottom of the visible area within its containing block. As a result, it never encounters the necessary threshold to become sticky.

To demonstrate how "bottom:0" works with "position:sticky," we can give a large margin to the "block" element, moving it off the screen. Once we start scrolling, we can observe that the "move" element starts sticking to the bottom of the visible screen when the "block" element scrolls past the top of the browser window.

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