Tips of using `cdkScrollable`

Element should Scrollable

Scrollable means content render size is bigger than Element size. A common mistake is not set container element size,
then container element never scrollable. Although overflow: auto is set.

Mark Scrollable Container Element with cdk cdkScrollable Directive

cdkScrollable provides .elementScrolled event triggered when scroll state changed, .scrollTo() method to change scroll position.

.elementScrolled event Outside Angular Context

For performance reason, .elementScrolled runs outside Angular runtime context, do not triggers Change Detection. To change
Angular bound property, wrap the code inside NgZone.