What is the theme in She Walks in Beauty by George Gordon Byron, Lord Byron?

Lord Byron's poem "She Walks in Beauty" was written in praise of a beautiful woman. History holds that he wrote it for a female cousin, Mrs. Wilmot, whom he ran into at a party in London one night when she was in mourning, wearing a black dress with glittering sequins. The poem uses images of light and darkness interacting to describe the wide spectrum of elements in a beautiful woman's personality and looks.