Over the last few years, Jobsite Theater shows have come to be among the best designed in the Bay area. One important reason is the work of Katrina Stevenson a long-time Jobsite regular who regularly excels as a costumer. Stevensons work was particularly noticeable in the avant-garde Serpent by Jean-Claude van Itallie: She placed the eight-member cast in flowing gray shirts and loose-fitting pants that announced immediately the ritualistic and nonrealistic intentions of the script. Her work was equally impressive in Woman in Mind, in which the clothing of the heroines real family was as dowdy and stuffy as her fantasy familys was crisp and attractive. Jobsite has found a real gem in Stevenson: She has intelligence and imagination and a sense of humor. Not a bad combination.