This is box A.

justify-self: stretch

This is box B.

justify-self: end

This is box C.

justify-self: start

This is box D.

justify-self: center

Each of the boxes on the left has a grid area of 3 columns and 3 rows (we're counting the gutter col/row). So each covers the same size area as box A.

The justify-self property is used to justify the content inside the grid-area.