Gaps between rows of flex items

A

BB

CCC

DDDD

EEEEE

FFFFFF

GGGGGGG

HHHHHHHH

IIIIIIIII

HHHHHHHH

GGGGGGG

FFFFFF

EEEEE

DDDD

CCC

BB

A

BB

CCC

DDDD

EEEEE

FFFFFF

GGGGGGG

HHHHHHHH

IIIIIIIII

HHHHHHHH

GGGGGGG

FFFFFF

EEEEE

DDDD

CCC

BB

A