Scroll container

Allows for vertical scroll within the element, enabled by the contain: size property/value. This allows it to be easily used in flex containers (e.g. stretched items across the height of the parent).

NOTE: always test the implementation in various use cases. For instance, on this site, the main content uses this class. However, on smaller screens, the contain: size needs to be replaced with contain: none, as the height would otherwise not fill the available space (due to flex-wrapping).