I don't know if my native languages worry about genders (I never thought of it) haha. I just thought you may do in Russian. I feel like so many things have genders for you, like такая being in the feminine when in english you don't specify any gender ("I am so happy" => so has no gender).
это is used during general/neutral statements like when saying 'it/this is a book'. But if you are being more specific about and object, then это turns into an adjective. All adjectives have to agree with the case, gender and number of the object(s). In this case, box is feminine and so это becomes эта.