In short, because of CL https://chromium-review.googlesource.com/c/chromium/src/+/1252682 (currently reverted but needs to reland in M72), all nested flexboxes will have min-height: auto. Therefore OOBE code (and all other web-ui code using nested flexboxes) needs to explicitly add min-height: 0 to mitigate the effect.
alemate@: please suggest on where to look at.
See issue 596743 and issue 891988 for details.
Comment 1 by wzang@chromium.org
, Oct 9