Flexbox default settings with children with auto-margins
Flexbox default settings with children with no margins

Horizontal align center (vertical stretch is default behavior)

Horizontal align center, vertical align center

Horizontal align center, vertical align top

Change direction to vertical, align settings keep their CSS values, but change names to fit the new situation

Flexbox vertical align center, but red and blue override with align buttons

Change orientation to vertical, overrides stay
(container height enlarged to demonstrate centering)