Style Secret: Trim and RickrackIn preppy design, details matter. Trims, from grosgrain ribbon to piping to pom-poms, add a polished touch to upholstered furnishings, window treatments and lampshades. The most important rule of thumb: Keep it tasteful. Think plain and modest, not overblown and in-your-face. Updated twist: To steer clear of fussiness, limit the number of trims you incorporate into a single space. The dainty lamp above, for example, is balanced by sleeker accents in the same color family for a streamlined look.