Пример использования свойства align-content

align-content: stretch;

A

B

C

D

E

F

align-content: flex-start;

A

B

C

D

E

F

align-content: flex-end;

A

B

C

D

E

F

align-content: center;

A

B

C

D

E

F

align-content: space-between;

A

B

C

D

E

F

align-content: space-around;

A

B

C

D

E

F