We've been wanting to include padding in the scrollable overflow area (to provide the specified space between the content and the border in all cases, not just when there's no overflow) in general, but we're constrained by compat in the general case. Florian points out that we're not so constrained for Grid/Flexbox, so maybe we should consider fixing this in Grid/Flexbox in general, not just for 'align-content: not-normal'.