CSS position sticky not working -- common reasons

position: sticky has no effect. Element scrolls normally instead of sticking. Works in some containers but not others.

Check all of these: (1) Must have a threshold: top, bottom, left, or right (e.g., top: 0). (2) Parent cannot have overflow: hidden, auto, or scroll (this creates a new scroll context). (3) Parent must have enough height for scrolling. (4) Cannot use sticky inside a table without border-collapse. (5) Ancestor with overflow clips the sticky context. Debug: remove overflow from all ancestors one by one until sticky works.

Sticky elements stick within their containing block (nearest scrolling ancestor). If any ancestor has overflow set, that becomes the scrolling context, and if it does not scroll, sticky has no effect.