ДЕМО-1
(свойство justify-content для строк)

justify-content: flex-start

justify-content: flex-end

justify-content: center

justify-content: space-between

justify-content: space-around

justify-content: space-evenly

ДЕМО-2
(свойство justify-content для столбцов)

justify-content: flex-start
justify-content: flex-end
justify-content: center
justify-content: space-between
justify-content: space-around