Why Does `bottom: 0` Sticky Positioning Behave Differently Than MDN\'s Description?

When Specifying bottom: 0 for Sticky Positioning, Why Does It Differ From MDN's Description?

The position:sticky property introduces a hybrid behavior between relative and fixed positioning. It mimics a relative position until a specified threshold is reached, at which point it transitions to a fixed position.

However, in your code snippet where bottom: 0 is set, the behavior appears to be reversed from what is described in MDN's article. The element starts as fixed and transitions to relative after scrolling past a threshold.

The reason behind this discrepancy lies in the wording of MDN's definition:

"Sticky positioning can be thought of as a hybrid of relative and fixed positioning. A stickily positioned element is treated as relatively positioned until it crosses a specified threshold, at which point it is treated as fixed until it reaches the boundary of its parent."

The key phrase here is "until it crosses a specified threshold." In your code, the element already crosses the specified threshold (the bottom of the viewport) when the page is initially rendered. Therefore, it enters the fixed positioning state immediately, even though bottom: 0 indicates that the threshold should be transitioning from relative to fixed.

In summary, when specifying bottom: 0 for a sticky element, it first starts fixed because the threshold is already reached, and then it transitions to relative when the element is scrolled back up past the bottom of the viewport. This behavior is consistent with the MDN definition, but the language used can be somewhat confusing.

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