Grid Layout and Flex Layout use automatic minimum sizes (min-content, by default, but depending on the specified min-width/min-height) to prevent grid items and flex items from shrinking too small to be usable. There's an exception to the use of min-content for grid/flex items which have overflow set on them, since authors expect those to shrink below their min-content size. But this exception doesn't follow through to descendants of the grid/flex item, resulting in confusion and frustration for authors. Issue #1777 was filed as a result of such confusion, and Dave Rupert posted http://daverupert.com/2017/09/breaking-the-grid/ discussing the problem.

This issue is filed to look into ways to ameliorate the problem: if we can make things Just Work as authors expect, that would be better! Of course Flex and Grid should be affected analogously, thus tagging them both in.