* grow banner when overscrolling
* add blurview
* make backdrop blur as it scrolls
* add activity indicator
* use rotated spinner instead of arrow
* persist position of back button
* make back button prettier
* make blur less jarring
* Unify effects
* Tweak impl
* determine if should animate based on scroll amount
* sign comment
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Co-authored-by: Dan Abramov <dan.abramov@gmail.com>
Samuel Newman