.offset-N (1 to 11, with infixes) adds a left margin of N twelfths. Offsets add to the column's width, so col-4 offset-9 exceeds 12 units and wraps. Often an auto margin is simpler: .ms-auto on a column absorbs all free space to its left, pushing it to the right edge whatever its width. To spread columns that do not fill 12 units, put justify-content-center, -between, -around or -evenly on the row, and align-items-* aligns them vertically. The next listing uses both offset-4 and ms-auto.