Scrollable areas - add dynamic shadows based on scroll position

From @jamestalton, I wanted to create an issue to track a request I've heard from James a few times. It would be super cool if PF was able to add shadows to scrollable regions dynamically. A good example we could currently work with is scrollable page sections. You designate a page section as .pf-m-overflow-scroll, and by default, it looks like any other page section. However, if its content is taller than the section, it will automatically add a scrollbar and the content becomes scrollable. PF could detected that there is overflow and added a shadow dynamically. Currently users can add shadows themselves by adding .pf-m-shadow-bottom (one for a top shadow, too) to the preceding page section, but that class adds a static shadow. If you add it because the section below has the potential to scroll, but doesn't scroll because there is no overflow content, the shadow appears unnecessarily.

Some questions:

• Currently a user could wire this up themselves, but should PF provide this ability?

• Would this be enabled for all scrollable regions? Sounds like that has the potential to create a lot of work to implement/maintain.

• Is there any kind of performance cost?

• Are there other cases for dynamic shadows - for example, adding a shadow only once you've scrolled a little bit? What's the LEO for that and does it come with performance costs?

Anything else you'd like to add @jamestalton?

Jira Issue: PF-1775

Beginne mit den verlinkten Seitensektionen overflow-scroll demo und prüfe, wie sich .pf-m-overflow-scroll und .pf-m-shadow-bottom derzeit verhalten. Kläre, ob dynamische Schatten allgemein oder nur auf Seitensektionen angewendet werden sollen, einschließlich der Erwartungen an die Performance und der gewünschten Zustände beim Scrollen. Als abgeschlossen gilt die Aufgabe, wenn Umfang und Verhalten vor Beginn der Implementierung vereinbart sind.