I rather like
position: sticky;. It has practical use cases. I think of things like keeping a table of contents in a sidebar of a long article, but as a fairly simple implementation and without risk of overlapping things in awkward ways. But Elad Shechter is right here: it's not used that much — at least partially — and probably because it's a bit weird to understand.
I like how Elad explains it with a "Sticky Item" and a "Sticky Container." The container needs to be large enough that scrolling is relevant and for the stickiness to do anything at all.
There are other gotchas, too. I feel like every time I try
position: sticky; in a real context, I have about a 30% chance of it working. There always seems to be some parent/child relationship thing that I can't quite work out to prevent overlaps. Or, there is some parent element with
overflow: hidden;, which, for reasons unbeknownst to me, breaks this.