Costa is renowned for her distinctive drawing style, distinguished by "characterized forms and bright colours.
She enjoyed drawing ever since her childhood, and at twelve she illustrated her first book, titling it Il pesciolino piccolo.
She collaborated with UNICEF for the illustration of Christmas cards, and designed several baby clothes lines for Benetton.
[11][12] A TV series based on Costa's character Julian Rabbit debuted on Rai YoYo in 2017.
[10] Costa's direct style is characterized by "smooth lines, black stroke as an outline, bright colors, and happy and radiant characters.
[9] Her best known characters are Olga the Cloud (La nuvola Olga), Blue Bear (Orso Blu), Catherine the Goose (L'oca Caterina), Theodora the Witch (La strega Teodora), John the Tree (L'albero Giovanni or El árbol Juan), Margaret the Teacher (La maestra Margherita), Cats (I gatti), Mr Kite (Il signor Aquilone), and Julio Bunny, or Julian Rabbit.
[14] Julian Rabbit, who is the title character of the series airing on Rai YoYo, has been described as "an antihero par excellence," who is shy and awkward, but "loves to surround himself with friends.
"[4] Speaking of the TV series, whose key message is mutual aid, Costa has stated: "[Julian the Rabbit's] stories teach kids that you get things done only with the help of friends.
[14] Costa's books are often used to introduce kids to reading in Italy, and have been used for this purpose to some extent also in other countries, including the United States, in Chicago's Italo-American community.