Too Long; Didn't Read
Position Sticky will only "stick" to its container block, and only if this one is a scrolling-container. Stacking Context is the three-dimensional conceptualization of HTML that it traduces to "What will it render first?" If things are in the same place, whatever is rendering last is what you will see. The stacking context will usually change every time you are not using a "static element" in one or another way. When you start scrolling and get to that 50px the element will switch to fixed right in that place.