Remove the two slashes in front of the justify-content value you want to test.

A
BBB
CCC
DD
EEEEEEEE
FFFFF
GGGGGGG
H
III

justify-content: center; ⤴

A
BBB
CCC
DD
EEEEEEEE
FFFFF
GGGGGGG
H
III

justify-content: space-between; ⤴

A
BBB
CCC
DD
EEEEEEEE
FFFFF
GGGGGGG
H
III

justify-content: space-around; ⤴