A utility is a single-purpose class: .p-3 sets padding and nothing else. Nearly every utility uses !important, so it wins over component CSS, and responsive ones take a breakpoint infix: .float-md-end floats from 768 pixels up. Bootstrap 5 2,007 replaced left and right with start and end (.ms-*, .end-0), which flip on right-to-left pages. CSS explains the underlying CSS.