Align the Track Collection
Content alignment distributes spare room around the grid as a whole.
Start
A
B
C
D
justify-content: start packs tracks at the inline start; align-content: start packs them at the block start.
Center
A
B
C
D
The fixed-size tracks move together to the center. Items still stretch inside those tracks by default.
Space between
A
B
C
D
space-between places spare room between the tracks. Content alignment has no visible effect when the tracks already fill the container.