The justify-content property is a sub-property of the Flexible Box Layout module. It defines the alignment along the main axis. […]

.element { justify-content: center; }

The justify-items property is a sub-property of the CSS Box Alignment Module which basically controls the alignment of grid items […]

.element { justify-items: center; }

The justify-self property aligns an individual element, overriding its parent current align-items value.

.element { justify-self: start; }