.lead makes an opening paragraph larger (1.25rem) and lighter. .mark and .small give any element the look of <mark> and <small>, and .initialism shrinks an abbreviation and uppercases it. Utilities such as .fw-semibold, .fst-italic, .text-uppercase and .text-decoration-line-through cover the rest (CSS explains the CSS). Prefer the semantic element when meaning matters to screen readers, and the class when you only want the look.