* Hide spinner on cart's "proceed to checkout" button when page unloads
This is required because of a feature of Safari where the page state is saved, including all class names, when a transition occurs. Navigating using the back button restores the page to that cached state, so the spinner class remains on the button. Resetting the state just before the page gets cached stops this from happening.
* Change comment case to sentence case.
* Shown express payment methods in Cart block
* Fixes
* Create usePositionRelativeToViewport hook
* Typo
* Style fixes
* Remove footer push div
* Styling fixes
* Improve code clarity
* Split ExpressCheckoutFormControl into two components
* Rename visibilityObserver to referenceElement
* Replace 'useEffect' with 'useLayoutEffect'
* Add tests for usePositionRelativeToViewport
* Self-closing div
* Add explanatory comment
* Create a shim for IntersectionObserver
* Update express payment components class names
* Add todo comment to remove IntersectionObserver shim when we drop IE11 support
opr
Darren Ethier
Albert Juhé Lluveras
Mike Jolley