A container simply corresponds to a <div> tag in the resulting HTML and can be used to add, for example, classes.
A scroll container is a widget that can have up to five regions that can scroll independently.
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You can add regions to a scroll container, when you put your data inside the scroll container, there will be a scrollbar per region (if the data inside the region can not be displayed without it/screen size matters). Scroll containers should be the top level widget, afaik you can not use more than one scroll container widget on the same page.