FSE: Sticky headers styling improvement suggestion

In classic, we have a sticky headers option. We properly persist that setting and styling-wise, they are pretty similar. The FSE header is slightly larger making the nature of the sticky header much more imposing, however. It's not necessary but it would be very cool if we could style this header to shrink with an animation when the user scrolls down.

**Sticky headers**

Here is an example with a smooth transition state.
https://codepen.io/iamsaief/pen/eYZRZPB